Start of real key locking
Next step of real locking ...
Real locking starts to work for GBM, DRF2, GLM1, GLM2

Lockable.update takes the Job key doing the update.
SharedTreeBuilder locks & unlocks the input datasets.
DGLM locks & unlocks the xval models.
More locking work

GLM1 read-locks input datasets
Pass Futures thru Lockable.delete
Locking fixes for lots of algos

KMeans, KMeans2, RF1, a bunch of RF tests
Exec2 is a work-in-progress still
Actually Lock and Unlock, plus global Key gather

Lock collisions still cause death tho
TaskSendKey to "push" a Key to some other node.  Used to gather keys
across the cluster for a global view.
Rename H2O.keySet to H2O.localKeySet.
Add H2O.globalKeySet
Value.backend() vs _persist&BACKEND
Another UKV remove for RF1
Add a locking / overlap test, & logging

-Dlog.LOCKS=true adds locking logging
Correct spelling
Merge
Change locked-error strings

Also fix bug with locking & autoframing & exec2
Merge