Filter comment classes

Limit to comment, bypostauthor, alt, thread-alt as appropriate.

Fixes #14
Fix custom_classes
Adjusting for WordPress Coding Standards
Merge branch 'refs/heads/master' into t/merge

Conflicts:
	collaborate/inc/html-tidy.php
Merge pull request #18 from peterwilsoncc/PW/filter-comment-classes

Filter comment classes