MAHOUT-1298: SparseRowMatrix,SparseColMatrix: optimize transpose()

Squashed commit of the following:

commit 809fa0105897113e44f7e55af611ed61d1746cb8
Merge: 9f963f8 21486b9
Author: Dmitriy Lyubimov <dlyubimov@apache.org>
Date:   Tue Jul 30 22:51:53 2013 -0700

    Merge branch 'trunk' into MAHOUT-1298

commit 9f963f83b942c2bccade9dfd860ef2ff19687bbc
Author: Dmitriy Lyubimov <dlyubimov@apache.org>
Date:   Mon Jul 29 16:53:12 2013 -0700

    Reverting whatever changes to SparseRowMatrixTest

commit 69e8c7655939ad3fe3072422b70e6fccfd6ce946
Author: Dmitriy Lyubimov <dlyubimov@apache.org>
Date:   Mon Jul 29 16:47:13 2013 -0700

    implementation; specific tests are not required (already implemented in abstract matrix test)

git-svn-id: https://svn.apache.org/repos/asf/mahout/trunk@1508733 13f79535-47bb-0310-9956-ffa450edef68