Merge remote-tracking branch 'upstream/develop' into develop

* upstream/develop:
Don't use a bad 2.10 version
Alternate approach to wiring up the counters
Fix typo
Move the keepAlive to the job class.

Remove the logger statements if flowProcess isn't defined. The sys.error in place means these statements will never be hit with a null.
First sketch at a sketch join
implicit evidence must come first
make some things private, avoid divide by zero in Sketched
Random needs seed
add some comments about maxReplicas math
"Require" sources in JobTests to have a mock buffer.

This is just adding an error message to inform users writing JobTests that they need to
provide buffers for every source used in the job.
Merge pull request #759 from daisyzhou/develop

"Require" sources in JobTests to have a mock buffer.
Merge pull request #756 from twitter/fix210ver

Don't use a bad 2.10 version
Review comments
Move the UniqueID case class out of the Job class to avoid serializations of it grabbing a reference to its parent
Move the job conf variable name to be a constant in the Job object
Make the stats holders not need to be object globals
Resolve merge conflict
address PR comments
BDD DSL to test pipe transformations (adapted from https://github.com/galarragas/ScaldingUnit)