Fixes #2216 -- Added extra tests for model validity, and cleaned up warning...

Fixes #2216 -- Added extra tests for model validity, and cleaned up warning messages for existing tests. Models are now invalid if the query string required to access a field (or related object) would clash with the name of another field (or related object). Previous tests only checked the accessor names, not the query string.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@3215 bcc190cf-cafb-0310-a4f2-bffc1f526a37