NOJIRA: distributed context property must really be public for engine-agnostic consumers
MAHOUT-1529(e): Move dense/sparse matrix test in mapBlock into spark (Anand Avati via dlyubimov)
All math-scala, spark tests are  passing.
this closes apache/mahout#29

Squashed commit of the following:

commit 1e3cdb68198636c9f38f2d41d782d12edba7a2f7
Author: Anand Avati <avati@redhat.com>
Date:   Mon Jul 14 17:20:09 2014 -0700

    MAHOUT-1529: Move dense/sparse matrix test in mapBlock into spark/

    In h2o engine, the Matrix provided to mapBlock() is an instance of
    "H2OBlockMatrix extends AbstractMatrix", and neither a DenseMatrix
    nor SparseMatrix. H2OBlockMatrix is a 0-copy virtual Matrix exposing
    just the partition's data (created at almost no expense), and creates
    a copy-on-write Matrix only if modified by the blockmapfunction.

    So these two tests are failing with h2obindings. Hence moving these two
    tests into spark module.

    Signed-off-by: Anand Avati <avati@redhat.com>
MAHOUT-1595: MatrixVectorView - implement a proper iterateNonZero() (Anand Avati via dlyubimov)
this closes apache/mahout#25

Squashed commit of the following:

commit eb2aa35da282b8955907fcd1ef358e825a100e95
Author: Anand Avati <avati@redhat.com>
Date:   Wed Jul 9 14:29:13 2014 -0700

    MAHOUT-1595: MatrixVectorView - implement a proper iterateNonZero()

    Previous implementation was broken as it was just calling iterator()

    Signed-off-by: Anand Avati <avati@redhat.com>