Changed the database engine environment variable to take a full dotted path to backend, to allow use of engines not packaged with Django.
Workaround for mysql.connector.django, which doesn't make _mysql_storage_engine a property on its database features class.
Removed dependency on six, allowing compatibility with earlier Django versions.
Updated travis ci config and testing settings to include mysql-connector database backend.
Merge pull request #59 from gdub/mysql-connector

Added testing compatibility with Oracle's mysql-connector-python (and other backends not packaged within Django)