MAHOUT-1580 Optimize getNumNonZeroElements() closes apache/mahout#17
MAHOUT-1573: More explicit parallelism adjustments in math-scala DRM apis; elements of automatic parallelism management

This closes apache/mahout#13.

Squashed commit of the following:

commit de03a6aa8361424ee8fb776f995fbe1b811e0ccd
Author: Dmitriy Lyubimov <dlyubimov@apache.org>
Date:   Wed Jun 18 14:22:46 2014 -0700

    doc

commit f399f7a4dc61905ef05d9944dbd2e5a4c31a654b
Merge: b02cf18 45d8803
Author: Dmitriy Lyubimov <dlyubimov@apache.org>
Date:   Wed Jun 18 14:18:35 2014 -0700

    Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/mahout into MAHOUT-1573

commit b02cf18dac608e2f969a845efd7ee35a3a5bd0e0
Author: Dmitriy Lyubimov <dlyubimov@apache.org>
Date:   Wed Jun 18 14:18:03 2014 -0700

    switching to par(...) api

commit 06bb4bcdedb3c5aac50a44ddec3957f1ed12d808
Author: Dmitriy Lyubimov <dlyubimov@apache.org>
Date:   Fri Jun 6 23:05:12 2014 -0700

    pom fixes to fix tests (spark hadoop dependencies must precede that of mahout-math's for tests to run correctly)

commit 1e6e3f87ffab5897569fea94c643da2bdbb59e33
Author: Dmitriy Lyubimov <dlyubimov@apache.org>
Date:   Fri Jun 6 22:15:33 2014 -0700

    remove any special handling of Par in rewrites

commit 2f3b4f5bac901ec152453473d4982cb9b6e5d651
Author: Dmitriy Lyubimov <dlyubimov@apache.org>
Date:   Fri Jun 6 16:33:27 2014 -0700

    + auto_|| operator

commit 2733002f4b5db3d5114a440b03967d954a3738e9
Author: Dmitriy Lyubimov <dlyubimov@apache.org>
Date:   Fri Jun 6 15:56:26 2014 -0700

    explicit parallelism adjustment levers exact_|| and min_||

commit cf7f18b4af4ad043d2bdcefeeda15031fa018543
Author: Dmitriy Lyubimov <dlyubimov@apache.org>
Date:   Fri Jun 6 13:21:19 2014 -0700

    docs

commit 2f785109b9a52e748626ba46f5bc0a35ffc98e2c
Author: Dmitriy Lyubimov <dlyubimov@apache.org>
Date:   Fri Jun 6 13:02:11 2014 -0700

    Refactoring drmFromHDFS()
MAHOUT-1579 Implement a data model which can load data from hadoop filesystem directly
fix some things from Sebastian's comments
change the scope of miniDFSCluster's denpency to 'test'
remove miniDFSCluster's dependencies and test HadoopFSDataModel with RawLocalFileSystem
Merge branch 'HadoopFSDataModel' of https://github.com/HuangXiaomeng/mahout into HadoopFSDataModel