ACCUMULO-2171 Update CHANGES for 1.6.0-RC3
ACCUMULO-2171 Include missed issues for CHANGES for 1.6.0-RC3
Merge branch '1.6.0-SNAPSHOT'
ACCUMULO-2702 Create separate MR Client Opts

Separate the MR opts from the core client opts. There is plenty more
work to be done, but this is a reasonable first step in that direction.

We should probably be using a lot more composition than inheritance
overall, and this resulted in some slight code duplication, but the
change set would have been *much* more extensive otherwise.
ACCUMULO-1880 create mapreduce module