Beta (trunk) updates:
* Uninstall added to delete attachment metadata related to cached document thumbnails and the thumbnail images themselves.
* Completely reworked attachment metadata to more sustainably handle current and future needs.

git-svn-id: https://plugins.svn.wordpress.org/document-gallery/trunk@838775 b8457f37-d9ea-0310-8a92-e5e31aec5664