Cleanup Vec enum
MRTask2.invoke renamed .doAll
Minor miscounting in new C1xChunks
Remove empty file?
More distributed tree-building

Split out Tree from GBM.  Make it distributable, and a cleaner
abstraction.  Use the new Tree API in GBM.  Rename MRTask2.invoke to
doall.  Convert more GBM code to fluid-vec style.
New split-out distributable tree
Fix test for new C1NChunk compression
Merge branch 'master' of https://github.com/0xdata/h2o