Moved BagOfWordsVariable to variable. Cleaned up xcoref.
Fixed bug in ClusterEvaluation.
Merge branch 'remove-hcoref' of https://github.com/factorie/factorie into remove-hcoref

Conflicts:
	src/main/scala/cc/factorie/app/nlp/BackwardsCompat.scala
Cleaned up the remainder of BackwardsCompat and removed it.