Small style fix
Treat manager like an old-style class
Explicitly get queryset when using query methods
Treat ModelAdmin like an old python class
Specify ImportError class for exception handler
Removed some 1.3 compatability code
Stop overriding built-ins
Use loading module directly
Cleanup `history_form_view()`
Revert "Treat manager like an old-style class"

This reverts commit c5ed822f46d8ad09b5303ef24198e607d9c5dbd4.
Revert "Treat ModelAdmin like an old python class"

This reverts commit 669558204e5c7c6e806ffa41a2145b9b031d2c7b.
Merge pull request #134 from treyhunner/code-quality

Some cleanup