* Appllied patch for bug 1686, image metadata cache by Andrius Ramanauskas.

* Appllied patch for bug 1686, image metadata cache by Andrius Ramanauskas.
* Changed memcached invalidation style in this patch to recache instead of deleting, which is better for concurrency
* Added a fix for the media link problem, differnet to my fix for the same problem in REL1_4 but either should work.
* Fixed image deletion, it didn't work at all. Not sure when it was broken or if it's been reported. It was working in REL1_4. It was a trivial error.