changed unittest to call for compatibility with Python 2.6
changed unittest to call for compatibility with Python 2.6

sourcelair/mongoengine,prijindal/mongoengine,cogniteev/mongoengine,MakerReduxCorp/mongoengine,nicolascine/mongoengine,cogniteev/mongoengine,blaggacao/mongoengine,DavidBord/mongoengine,Catstyle/mongoengine,eli-b/mongoengine,touilleMan/mongoengine,starsirius/mongoengine,reallistic/mongoengine,iandd0824/mongoengine,MongoEngine/mongoengine,yarneo/mongoengine,gmacon/mongoengine,MRigal/mongoengine,RussellLuo/mongoengine,muhammad-ammar/mongoengine,9nix00/mongoengine,khallaghi/mongoengine,Davidrjx/mongoengine,ConsumerPhysics/mongoengine,gavincabbage/mongoengine,WingGao/mongoengine,larsbutler/mongoengine,ProgressivePlanning/mongoengine,nathanial/mongoengine,MakerReduxCorp/mongoengine,ms5/mongoengine,losintikfos/mongoengine,Davidrjx/mongoengine,jimmyshen/mongoengine