7034: probably_alive() failing when no birth-death

docstring fix

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@23053 4ae1f11a-8b86-4847-b8af-ab372f36d1fd
Add some UT for Date.set2_... and fix bugs

Cut and paste is evil ;-) fix bugs before I refactor the code...

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@23054 4ae1f11a-8b86-4847-b8af-ab372f36d1fd
raise DateError in set2_... if not is_compound()

refactor Date to always use is_compound instead of repeating
its logic everywhere

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@23055 4ae1f11a-8b86-4847-b8af-ab372f36d1fd
refactor set_yr_mon_day and set2_yr_mon_day

refactor common base

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@23056 4ae1f11a-8b86-4847-b8af-ab372f36d1fd