Fixes #2918 -- Clarified the db_prep_save logic for DateField and DateTimeField to prevent accidental conversion of non-datetime objects into strings, because SQLite doesn't appear to check for valid date format in a string used on an UPDATE of a datetime column.
Fixes #2918 -- Clarified the db_prep_save logic for DateField and DateTimeField to prevent accidental conversion of non-datetime objects into strings, because SQLite doesn't appear to check for valid date format in a string used on an UPDATE of a datetime column.


git-svn-id: 4f9f921b081c523744c7bf24d959a0db39629563@3960 bcc190cf-cafb-0310-a4f2-bffc1f526a37

aparo/django-nonrel,FlaPer87/django-nonrel,aparo/django-nonrel,FlaPer87/django-nonrel,FlaPer87/django-nonrel,aparo/django-nonrel