Move hashJoin and friends to TypedPipe
Don't convert back to TypedPipe from KeyedList until needed
Created a typed wrapper for Checkpoint and added tests for it
Merge pull request #722 from ccsevers/typed_checkpoint

Created a typed wrapper for Checkpoint and added tests for it
Merge pull request #721 from twitter/fix-hash

Move hashJoin and friends to TypedPipe
Fix compile bug with scalding-commons
Merge pull request #724 from twitter/stay-grouped

Looks good. join join join sounds like a really useful next thing.