make it easier to support multiple backends in the future
* src/RelLib.py: broke out support for database class to
make it easier to support multiple backends in the future
* src/AddSpouse.py: better support for gay unions
* src/ChooseParents.py: better support for gay unions
* src/FamilyView.py: better support for gay unions
* src/Marriage.py: better support for gay unions
* src/ReadXML.py: better support for gay unions
* src/gramps.glade: better support for gay unions
* src/gramps_main.py: better support for gay unions
* src/Check.py: better support for gay unions
* src/ReadGedcom.py: better support for gay unions
svn: r3302
