Merge pull request #476 from branch bwf-mr-const-hash

Squashed commit of the following:

commit 0c07454626517c6f26013ea373cbcf516e3033ee
Author: Bryan Fink <bryan@basho.com>
Date:   Sat Feb 2 10:17:43 2013 -0500

    cleanup and rework contant reduce hash

    Builds on commit in #475 with more documentation, variable name cleanup,
    and a more failure-tolerant up-vnode-finder strategy.

commit 58040e86689d93ee68abb16744b1d8598a9a9cd2
Author: Dreyk <gunin@satissoft.ru>
Date:   Fri Feb 1 13:44:49 2013 +0400

    Update src/riak_kv_mrc_pipe.erl

    Reduce phase must be started on live node.