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>