Partial support for variable-sized bins in MantelCorrelogram class.
Add is_valid_git_refname and is_valid_git_sha1

Given the great variability that exists between versions of git, this
functions validate the output returned from the git commands used to
retrieve the current branch name (refname) and the current SHA.

The function get_qiime_library_version was updated to make use of these
functions.

The module was updated accordingly.

This should fix issue #603.
Modified the compare_alpha_diversity library, script, and tests to resolve issue #597.
Merge branch 'master' into mantel_correlogram_bins
Added MantelCorrelogram._find_row_col_indices(), which is necessary for variable-sized bins.
Added variable-size bin support to MantelCorrelogram._find_distance_classes().
Added --variable_size_distance_classes option to compare_distance_matrices.py script.
Fixed a couple of border-case bugs and added tests for them.
Added notes to changelog; reverted a few comments I didn't mean to add.
Merge pull request #612 from wdwvt1/compare_alpha_diversity_fixes

Modified the compare_alpha_diversity library, script, and tests to resol...
Merge pull request #609 from ElDeveloper/git_version

Add is_valid_git_refname and is_valid_git_sha1
Merge pull request #627 from jrrideout/mantel_correlogram_bins

Added support for variable-size distance classes in Mantel correlogram.
Merge branch 'master' into timeseries_filtering

Conflicts:
	ChangeLog.md