DepParser1.train: Add feature pruning with cutoff 3.
DepParser2.serialize: Use foreachElement for weight sparsification,
rather than AdaGradRDA.copy followed by +=.
Merge branch 'master' of git@github.com:factorie/factorie.git
Merge pull request #5 from andrewmccallum/master

DepParser2.serialize: More efficient sparsification.  DepParser1.train: FeaturesDomain.trimBelowCount(3)