Fix MultilingualQUerySet custom inheritance.
Fix MultilingualQUerySet custom inheritance - part 2.
Revert "Added a workaround for abstract models not being handled correctly."

This reverts commit a3e44c187b5abfa6d9b360cecc5c1daa746134f5.
Merge pull request #125 from zlorf/update_fix2

Fix for custom QuerySets.