GrampsDbBase; (_get_obj_from_gramps_id,_find_from_handle): Only
read data if the key exists.
* src/GrampsDb/_GrampsDbBase.py (get_gramps_ids,has_gramps_id):
Add methods; (check_*_from_handle): Add methods that make sure
that object exists in the db, create as necessary, but do not read
if it exists; (_check_from_handle): Add lower-level method;
(_find_from_handle): Only read data if the key exists.
* src/GrampsDb/_GrampsInMemDB.py (get_gramps_ids): Move to
GrampsDbBase.
* src/GrampsDb/_ReadXML.py: Multiple improvements.
svn: r5858
* src/GrampsDb/_GrampsBSDDB.py: More XML export fixes.
* src/GrampsDb/_GrampsDbBase.py: More XML export fixes.
* src/GrampsDb/_GrampsInMemDB.py: More XML export fixes.
* src/GrampsDb/_WriteXML.py: More XML export fixes.
svn: r5842
