* src/EditRepository.py: modified to use find_backlink_handles and fixed subtle bug
* src/RelLib/_Source.py: added reporef_list to referent object lists so that backref
are put in reference_map
* test/GrampsDb/GrampsDbBase_Test.py: added unittest for source/reference backlinks
* test/GrampsDb/GrampsDbTestBase.py: added unittest for source/reference backlinks
svn: r5616