Fixed #10660 -- `GeometryField` no longer requires `srid`/`null` keywords, and...

Fixed #10660 -- `GeometryField` no longer requires `srid`/`null` keywords, and now respects `required`; coordinate transformations now done inside `gis.forms.GeometryField` -- benefit being that `OSMGeoAdmin` no longer requires 900913 entry in `spatial_ref_sys` thus enabling it to work with MySQL/Oracle spatial backends; added tests for geographic forms.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@10634 bcc190cf-cafb-0310-a4f2-bffc1f526a37