MAHOUT-1529 closes PR #1

Squashed commit of the following:

commit e7b27280333fe12c94f3f5675c876f56e9e60728
Author: Dmitriy Lyubimov <dlyubimov@apache.org>
Date:   Tue May 27 11:01:13 2014 -0700

    License, comments

commit bfca581389d91fb9c41db8c49e256ff694335fd1
Author: Dmitriy Lyubimov <dlyubimov@apache.org>
Date:   Fri May 23 16:07:01 2014 -0700

    Fixing  shell

commit c3b8aa4bf7d8939aa0800ce12b7f63e01f9686b9
Author: Dmitriy Lyubimov <dlyubimov@apache.org>
Date:   Fri May 23 13:36:20 2014 -0700

    - MahoutContext

commit a6461ac22a46793ab0bcdfcafe827d808f9e1810
Author: Dmitriy Lyubimov <dlyubimov@apache.org>
Date:   Fri May 23 12:13:40 2014 -0700

    rebasing changes in MAHOUT-1529 branch on to new git master (applied thru selective patching, may, but hopefully, doesn't revert any commits in between in spark/ and math-scala/ modules
MAHOUT-1529 closes #1
(nojira) Changelog updates
Tests for RHS and mutate.
+select
mixing integral and named subscripts
should return DFrameLike
Playing with messy things
speed tests using Unsafe..