6960: Error merging citations

Back-port my work on this bug from gramps40.
Unfortunately, the tests on gramps34 still fail (they pass
on gramps40/trunk), but the repro steps marked by Nick
in the bug succeed, so I shall stop here :)

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/branches/maintenance/gramps34@22965 4ae1f11a-8b86-4847-b8af-ab372f36d1fd
Fix regular expressions in sidebar filters

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/branches/maintenance/gramps34@22966 4ae1f11a-8b86-4847-b8af-ab372f36d1fd
6960: fix merging citations batch tool; sources

Back-port from gramps40 of r22971.

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/branches/maintenance/gramps34@22972 4ae1f11a-8b86-4847-b8af-ab372f36d1fd