Refactored `get_srid_info` to use the ORM (now possible since it's no longer...

Refactored `get_srid_info` to use the ORM (now possible since it's no longer used in `GeometryField.__init__`), and moved to `fields` module; removed unnecessary code.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@10493 bcc190cf-cafb-0310-a4f2-bffc1f526a37