6926: add partial dates (M/Y and Y), not just DMY

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@23166 4ae1f11a-8b86-4847-b8af-ab372f36d1fd
7068: undo french fallback to gregorian

French SDN conversion functions now accept an optional boolean
parameter that allows to block dates outside the republican period.
By default, calendar conversions are allowed.
Revert test blocked by r23139, it now passes!

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@23167 4ae1f11a-8b86-4847-b8af-ab372f36d1fd