move codecsource to core
begin to fix tests
Add scalding-commons in Build path and move CodecSource to scalding-core.
Fix sum in CheckpointSpect.
Add missing resolver from scalding-commons.
Add gmlcompression dependency into scalding-core.
Add twitter Maven resolver.
Refactor the Mode into a trait, add FlowState
Merge with develop, which has the scalding-commons build successfully.
More cleanups, address review
Reduce default spill threshold back to 100k
Add Scheme type casting in LzoTraits, for scala 2.10.0
Merge pull request #464 from twitter/mode-trait

Refactor the Mode into a trait, add FlowState
Clean some unnecessary code that was written before merge with develop.
Merge pull request #456 from twitter/feature/fix_commons_move_codec_source

Move codec source