MAHOUT-1280: moving UpperTriangularMatrix to mahout-math as well as adding Symmetric matrix as a first class citizen.

Squashed commit of the following:

commit 50d97093eff5416b7b644efaae159ea35d7e7279
Author: Dmitriy Lyubimov <dlyubimov@apache.org>
Date:   Wed Jul 17 23:35:49 2013 -0700

    Illegal like()

commit 7ce78c1dfc7b2c15fef787380e617b873df5890d
Author: Dmitriy Lyubimov <dlyubimov@apache.org>
Date:   Wed Jul 10 12:54:46 2013 -0700

    Bug fixes in constructor-by-vector

commit ef11cfa02727fb29b2533c0848734809f77f8a3e
Author: Dmitriy Lyubimov <dlyubimov@apache.org>
Date:   Wed Jul 10 11:22:06 2013 -0700

    Switching SSVD uses to UpperTriangular.

commit 3e73a8cd7ba32cb8696d76b93ec287540c710f68
Author: Dmitriy Lyubimov <dlyubimov@apache.org>
Date:   Wed Jul 10 10:55:11 2013 -0700

    Adding test for dense symmetric matrix asserting Eigen decomposition equivalent to that over a dense matrix.

commit 6fc530b75215c5ad1c0b5561ff3af724c6e48c6b
Author: Dmitriy Lyubimov <dlyubimov@apache.org>
Date:   Tue Jul 9 18:30:59 2013 -0700

    Moving UpperTriangular matrix to mahout.math; adding DenseSymmetric matrix.

git-svn-id: https://svn.apache.org/repos/asf/mahout/trunk@1507150 13f79535-47bb-0310-9956-ffa450edef68
Merge branch 'trunk' into MAHOUT-1281

Conflicts:
	core/src/main/java/org/apache/mahout/math/hadoop/stochasticsvd/SSVDHelper.java
	core/src/main/java/org/apache/mahout/math/hadoop/stochasticsvd/SSVDSolver.java