unicode name support broken, breaks etckeeper: bzrlib.errors.InvalidEntryName: Invalid entry name: snap-gnome\x2d3\x2d28\x2d1804-110.mount

Not sure whether this is properly a bug in
- bzr, for failing to handle names legal to filesystem
- etckeeper, for failing to wrap names known to be unusable by one of its version-control engines
- webkit, for daring to use filenames which break some tools
but I'm going with the bzr, fixing the issue at the level which avoids a larger class of problem

I don't use bzr, except for etckeeper, which installed it years ago as its default engine

On Ubuntu-19.10, I was adding packages with
  sudo apt install libwebkit2gtk-4.0-{37,dev,doc}
which invoked etckeeper to log the changes, leading to ...

bzr: ERROR: bzrlib.errors.InvalidEntryName: Invalid entry name: snap-gnome\x2d3\x2d28\x2d1804-110.mount

Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/bzrlib/commands.py", line 930, in exception_to_return_code
    return the_callable(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/bzrlib/commands.py", line 1121, in run_bzr
    ret = run(*run_argv)
  File "/usr/lib/python2.7/dist-packages/bzrlib/commands.py", line 673, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/usr/lib/python2.7/dist-packages/bzrlib/commands.py", line 697, in run
    return self._operation.run_simple(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/bzrlib/cleanup.py", line 136, in run_simple
    self.cleanups, self.func, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/bzrlib/cleanup.py", line 166, in _do_with_cleanups
    result = func(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/bzrlib/builtins.py", line 842, in run
    no_recurse, action=action, save=not dry_run)
  File "/usr/lib/python2.7/dist-packages/bzrlib/mutabletree.py", line 52, in tree_write_locked
    return unbound(self, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/bzrlib/mutabletree.py", line 453, in smart_add
    adder.add(file_list, recurse=recurse)
  File "/usr/lib/python2.7/dist-packages/bzrlib/mutabletree.py", line 764, in add
    inv_path)
  File "/usr/lib/python2.7/dist-packages/bzrlib/mutabletree.py", line 628, in _add_one_and_parent
    file_id=file_id)
  File "/usr/lib/python2.7/dist-packages/bzrlib/inventory.py", line 2234, in make_entry
    return factory(file_id, name, parent_id)
  File "/usr/lib/python2.7/dist-packages/bzrlib/inventory.py", line 422, in __init__
    super(InventoryFile, self).__init__(file_id, name, parent_id)
  File "/usr/lib/python2.7/dist-packages/bzrlib/inventory.py", line 222, in __init__
    raise errors.InvalidEntryName(name=name)
InvalidEntryName: Invalid entry name: snap-gnome\x2d3\x2d28\x2d1804-110.mount

bzr 2.8.0dev1 on python 2.7.16 (Linux-5.0.0-38-generic-x86_64-with-
    Ubuntu-19.04-disco)
arguments: ['/usr/bin/bzr', 'add', '-q', '.']
plugins: bash_completion[2.8.0dev1], builddeb[2.8.6], bzrtools[2.6.0],
    changelog_merge[2.8.0dev1], etckeeper[unknown], grep[2.8.0dev1],
    launchpad[2.8.0dev1], netrc_credential_store[2.8.0dev1],
    news_merge[2.8.0dev1], po_merge[2.8.0dev1], weave_fmt[2.8.0dev1]
encoding: 'utf-8', fsenc: 'UTF-8', lang: 'en_US.UTF-8'

*** Bazaar has encountered an internal error. This probably indicates a
    bug in Bazaar. You can help us fix it by filing a bug report at
        https://bugs.launchpad.net/bzr/+filebug
    including this traceback and a description of the problem.
etckeeper warning: bzr add failed
Committing to: /etc/
modified cups/printers.conf
Committed revision 2295.
Selecting previously unselected package libpsl-dev:amd64.
(Reading database ... 609849 files and directories currently installed.)
Preparing to unpack .../libpsl-dev_0.20.2-2_amd64.deb ...
Unpacking libpsl-dev:amd64 (0.20.2-2) ...
Selecting previously unselected package libsoup2.4-dev:amd64.
Preparing to unpack .../libsoup2.4-dev_2.66.1-1ubuntu0.1_amd64.deb ...
Unpacking libsoup2.4-dev:amd64 (2.66.1-1ubuntu0.1) ...
Selecting previously unselected package libjavascriptcoregtk-4.0-dev:amd64.
Preparing to unpack .../libjavascriptcoregtk-4.0-dev_2.26.2-0ubuntu0.19.04.1_amd64.deb ...
Unpacking libjavascriptcoregtk-4.0-dev:amd64 (2.26.2-0ubuntu0.19.04.1) ...
Selecting previously unselected package libwebkit2gtk-4.0-dev:amd64.
Preparing to unpack .../libwebkit2gtk-4.0-dev_2.26.2-0ubuntu0.19.04.1_amd64.deb ...
Unpacking libwebkit2gtk-4.0-dev:amd64 (2.26.2-0ubuntu0.19.04.1) ...
Selecting previously unselected package libwebkit2gtk-4.0-doc.
Preparing to unpack .../libwebkit2gtk-4.0-doc_2.26.2-0ubuntu0.19.04.1_all.deb ...
Unpacking libwebkit2gtk-4.0-doc (2.26.2-0ubuntu0.19.04.1) ...
Setting up libjavascriptcoregtk-4.0-dev:amd64 (2.26.2-0ubuntu0.19.04.1) ...
Setting up libpsl-dev:amd64 (0.20.2-2) ...
Setting up libwebkit2gtk-4.0-doc (2.26.2-0ubuntu0.19.04.1) ...
Setting up libsoup2.4-dev:amd64 (2.66.1-1ubuntu0.1) ...
Setting up libwebkit2gtk-4.0-dev:amd64 (2.26.2-0ubuntu0.19.04.1) ...
Processing triggers for man-db (2.8.5-2) ...
Processing triggers for doc-base (0.10.8) ...
Processing 3 added doc-base files...
bzr: ERROR: bzrlib.errors.InvalidEntryName: Invalid entry name: snap-gnome\x2d3\x2d28\x2d1804-110.mount

Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/bzrlib/commands.py", line 930, in exception_to_return_code
    return the_callable(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/bzrlib/commands.py", line 1121, in run_bzr
    ret = run(*run_argv)
  File "/usr/lib/python2.7/dist-packages/bzrlib/commands.py", line 673, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/usr/lib/python2.7/dist-packages/bzrlib/commands.py", line 697, in run
    return self._operation.run_simple(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/bzrlib/cleanup.py", line 136, in run_simple
    self.cleanups, self.func, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/bzrlib/cleanup.py", line 166, in _do_with_cleanups
    result = func(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/bzrlib/builtins.py", line 842, in run
    no_recurse, action=action, save=not dry_run)
  File "/usr/lib/python2.7/dist-packages/bzrlib/mutabletree.py", line 52, in tree_write_locked
    return unbound(self, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/bzrlib/mutabletree.py", line 453, in smart_add
    adder.add(file_list, recurse=recurse)
  File "/usr/lib/python2.7/dist-packages/bzrlib/mutabletree.py", line 764, in add
    inv_path)
  File "/usr/lib/python2.7/dist-packages/bzrlib/mutabletree.py", line 628, in _add_one_and_parent
    file_id=file_id)
  File "/usr/lib/python2.7/dist-packages/bzrlib/inventory.py", line 2234, in make_entry
    return factory(file_id, name, parent_id)
  File "/usr/lib/python2.7/dist-packages/bzrlib/inventory.py", line 422, in __init__
    super(InventoryFile, self).__init__(file_id, name, parent_id)
  File "/usr/lib/python2.7/dist-packages/bzrlib/inventory.py", line 222, in __init__
    raise errors.InvalidEntryName(name=name)
InvalidEntryName: Invalid entry name: snap-gnome\x2d3\x2d28\x2d1804-110.mount

bzr 2.8.0dev1 on python 2.7.16 (Linux-5.0.0-38-generic-x86_64-with-
    Ubuntu-19.04-disco)
arguments: ['/usr/bin/bzr', 'add', '-q', '.']
plugins: bash_completion[2.8.0dev1], builddeb[2.8.6], bzrtools[2.6.0],
    changelog_merge[2.8.0dev1], etckeeper[unknown], grep[2.8.0dev1],
    launchpad[2.8.0dev1], netrc_credential_store[2.8.0dev1],
    news_merge[2.8.0dev1], po_merge[2.8.0dev1], weave_fmt[2.8.0dev1]
encoding: 'utf-8', fsenc: 'UTF-8', lang: 'en_US.UTF-8'

*** Bazaar has encountered an internal error. This probably indicates a
    bug in Bazaar. You can help us fix it by filing a bug report at
        https://bugs.launchpad.net/bzr/+filebug
    including this traceback and a description of the problem.
etckeeper warning: bzr add failed