python-fixtures dependency is not installed

Installing testresources doesn't cause python-fixtures to be installed. This results in highly obscure failures like:

$ testr commands
'Could not import command module testrepository.commands.list_tests'

which largely render testr useless.

ProblemType: Bug
DistroRelease: Ubuntu 12.10
Package: python-testresources 0.2.4-1ubuntu1
ProcVersionSignature: Ubuntu 3.5.0-18.29-generic 3.5.7
Uname: Linux 3.5.0-18-generic i686
ApportVersion: 2.6.1-0ubuntu6
Architecture: i386
Date: Tue Nov 20 09:56:04 2012
MarkForUpload: True
PackageArchitecture: all
ProcEnviron:
 LANGUAGE=en_US:en
 TERM=screen
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: testresources
UpgradeStatus: Upgraded to quantal on 2012-11-17 (2 days ago)