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.
Make AAE rehash delete missing data from relevant hashtree

This change ensures that AAE does not attempt to continually repair
deleted keys that an AAE hashtree believes still exist.
Change AAE hashtrees to buffer/batch deletes

AAE already buffers writes and submits them as a single write-batch to
LevelDB for better performance. Since deletes are also valid batch
operations, this change buffers deletes alongside writes and submits
all operations as a single write-batch as necessary.

This change also fixes a potential bug in the previous approach that
could reorder a write to happen after a delete, even if the delete
occured after the write -- thus reviving a dead hash.
Merge pull request #478 from basho/jdb-aae-deleted
Merge branch '1.3'