MAHOUT-1583: cbind() operator for Scala DRMs
This closes apache/mahout#20

Squashed commit of the following:

commit 1baf3fcebf2cd49eb6487afe4eaed689653a3562
Merge: 41f0671 9bfb767
Author: Dmitriy Lyubimov <dlyubimov@apache.org>
Date:   Mon Jul 7 12:32:34 2014 -0700

    Merge branch 'master' into MAHOUT-1583

commit 41f0671c9ccca81883475437fe18056563c1f8ac
Author: Dmitriy Lyubimov <dlyubimov@apache.org>
Date:   Mon Jul 7 12:27:26 2014 -0700

    Adding assignment time comparison test

commit 6e115c87639ffb111b2e089d7ecdf0eaeecbb02b
Author: Dmitriy Lyubimov <dlyubimov@apache.org>
Date:   Mon Jun 16 18:42:42 2014 -0700

    + Licenses.

commit d3e905b5a92735822efe717f8b7a57c80bc56478
Author: Dmitriy Lyubimov <dlyubimov@apache.org>
Date:   Mon Jun 16 18:09:59 2014 -0700

    initial writeup