Restrict processing of POST requests for the plugin to the plugin page.

git-svn-id: https://plugins.svn.wordpress.org/photostream-sync/trunk@810866 b8457f37-d9ea-0310-8a92-e5e31aec5664
stable tag

git-svn-id: https://plugins.svn.wordpress.org/photostream-sync/trunk@810870 b8457f37-d9ea-0310-8a92-e5e31aec5664