Propagate merged authority record change to bibliographic record

Propagate merged authority record change to bibliographic record

Launchpad bug 688015 reported that the merge of authority records
resulted in the control number identifier in a controlled field
in a bibliographic record changing to the right value, but the
value of the field itself wasn't being changed.

The problem turned out to be a confusion of the "source" and
"target" values in the authority.merge_record() function. Once
that was straightened out, the merge updated the controlled
field as expected.

git-svn-id: svn://svn.open-ils.org/ILS/trunk@19032 dcc99617-32d9-48b4-a31d-7c20da2025e4