Merge pull request #543 from jdufresne/master

sqldiff: Remove MySQL workaround, causes more issues then it solves.
remove pypy from allowed failures list
Merge branch 'master' of https://github.com/django-extensions/django-extensions
Add support for unsigned numeric fields in MySQLDiff backend.

Query the information_schema.columns table to discover if an numeric
field is unsigned. Use that when returning the db_type. Add
AUTO_INCREMENT check to after the unsigned signed check so db fields
that are unsigned primary keys properly conflict with AutoField.

Fixes #544