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

* upstream/develop:
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
address PR comments
BDD DSL to test pipe transformations (adapted from https://github.com/galarragas/ScaldingUnit)
Merge branch 'develop' of github.com:twitter/scalding into develop

* 'develop' of github.com:twitter/scalding:
  "Require" sources in JobTests to have a mock buffer.
  Don't use a bad 2.10 version
  Fix typo
  Re-add mapValues to IdentityReduce
  make sure to push filterKeys mapside
  add filterKeys
  Add .filter to KeyedListLike
Make sure to set cascading.app.appjar.class so that cascading can find job classes on mappers/reducers
Used TypedSink in VersionedKeyValSource
Merge pull request #762 from themodernlife/develop

Issues using skinny jars, -libjars flag and com.twitter.scalding.Tool as the Main class
Merge pull request #763 from twitter/fix-versionedkvs

Used TypedSink in VersionedKeyValSource
start of a test for sketch joins
also test sketch left join
flesh out sketch join tests; still don't work in local mode
narrowed the problem with running local to TypedSelfLeftCrossTest
switch Sketched to use cross instead of leftCross to avoid bug
Removed useless import of scala.Tuple causing failure when testing with Scala 2.10.0. Added README.md file to document the usage of the BddDsl class
remove spurious toList, tweak and comment params on CMS for sketched