added foldByKey
restrict V type of foldByKey in order to retain ClassManifest; added foldByKey to Java API and test
Fuller implementation of foldByKey
whitespace cleanup
Merge branch 'master' of https://github.com/mesos/spark into foldByKey
Merge branch 'master' of https://github.com/mesos/spark into foldByKey
refactor foldByKey to use combineByKey
whitespace
Merge pull request #526 from markhamstra/foldByKey

Add foldByKey