Remove qiime.util.DistanceMatrix and unit tests
Remove DistanceMatrix usage from test_format.py

Also cleaned up related test code so that it uses mock stats results dictionaries. This makes the test code much simpler and decouples it from qiime.stats.
Merge branch 'master' into issue-829
Update stats.py, test_stats.py

Now uses SymmetricDistanceMatrix.
update compare_categories.py lib code
update compare_distance_matrices.py lib code
Merge pull request #1390 from jrrideout/issue-829

Replace qiime.util.DistanceMatrix with bipy.core.distance.SymmetricDistanceMatrix