added sample_count_by_category
using natural sort now
Changed exception to option_parser.error
renamed to print_metadata_stats.py
fixed version
Merge pull request #591 from wasade/sample_count_by_category

added sample_count_by_category
Added new function mean_alpha and tests

This function allows to compute the mean alpha diversity data at a given
rarefaction depth.
Updated script to handle collated alpha data

Collated alpha diversity files can now be used with this script, the
user is now able to specify a given depth to get the mean of the values
added to the mapping file.
Merge pull request #596 from ElDeveloper/collated_alpha_map

Collated alpha map
Adding functionality to calculate linear distance from a latitute/longitud point
Fixing a missing credit
Partial support for variable-sized bins in MantelCorrelogram class.
Fixing issues from pull request
Fixing wrong evaluation of max/min lat/long
Fixing error message for lat/long evaluation
Backported changes to rdp_classifier.py in PyCogent
Merge pull request #602 from antgonza/lat_long_distance

Adding functionality to calculate linear distance from Latitude/Longitude point
Fixing error with distance_matrix_from_mapping.py in Clout
Merge pull request #607 from antgonza/fix_for_distance_matrix_from_mapping_in_clout

Fixing error with distance_matrix_from_mapping.py in Clout
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.