Comment 9 for bug 1878984

I have a branch available here:

https://git.evergreen-ils.org/?p=working/Evergreen.git;a=shortlog;h=refs/heads/user/miker/lp-1878984-vandelay-preserve

From the commit message:

When processing a Preserve specification, vandelay.replace_field fails to account for the situation where the target record does not have any instances of the field to be preserved. This commit copies fields from the source to the target when there are no like target fields and the source fields are not restricted by a match requirement.

It additionally adds multi-subfield match requirement capabilities to the add_field and replace_field functions, as implemented in the branch submitted for LP#1901597 that does the same for strip_field.