Prepare for Github

git-svn-id: http://plugins.svn.wordpress.org/gallery-excerpt/trunk@960648 b8457f37-d9ea-0310-8a92-e5e31aec5664
Tested up to 3.9.1

git-svn-id: http://plugins.svn.wordpress.org/gallery-excerpt/trunk@960649 b8457f37-d9ea-0310-8a92-e5e31aec5664