Implementing change that will allow users to prefix taxon names with "tax_" in order to avoid potential collisions with the other parameters.

git-svn-id: http://plugins.svn.wordpress.org/document-gallery/trunk@1032193 b8457f37-d9ea-0310-8a92-e5e31aec5664
Various minor updates sitting in my workspace

git-svn-id: http://plugins.svn.wordpress.org/document-gallery/trunk@1032197 b8457f37-d9ea-0310-8a92-e5e31aec5664
* Adding post_type, post_status, and limit as possible attributes in shortcode
* Cleaned up DG_Admin in some places where logic was being duplicated

git-svn-id: http://plugins.svn.wordpress.org/document-gallery/trunk@1032329 b8457f37-d9ea-0310-8a92-e5e31aec5664