Modifications and test additions to resolve issue #1160
Modified test and function.

There is an untested function in this code that makes boxplots. The build failed because that function called the modified function from the previous commit.
Merge branch 'master' into issue_1160
Merge branch 'master' into issue_1160
Merge branch 'master' into issue_1160
Resolved @wasade's comments.
Modifications to incorporate new functionality

This commit uses the function @gregcaporaso wrote to reduce the size and runtime of the compare_alpah_diversity function which is the workhorse of this module.
Merge branch 'master' into issue_1160
Merge pull request #1256 from wdwvt1/issue_1160

Modifications and test additions to resolve issue #1160