Make sure that all uses of max_length in the test suite use values smaller...

Make sure that all uses of max_length in the test suite use values smaller than 255. If we use max_length > 255 the test suite can't be run on MySQL 4.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@10697 bcc190cf-cafb-0310-a4f2-bffc1f526a37