Code for a managed memcache engine

Hello! I'm adding some "features" at your module, and I'd like to tell you which and how. For that issues, I created a new engine, called "managed memcache" that inherits from the memcache one. This way I can keep experimenting and simply fall back to the old and glorious memcache engine if something fails. My engine does two things:
- it is aware of the global "cache" setting in drupal. This way I can use cacheset/get in all my modules and have a single point to activate/deactivate the cache functionality (debugging, weird behaviour, you know).
- it (partially) supports the wildcard cache_clear_all. I've borrowed some code from the flush() but there's some other work to do (read my FIXME)

So, this code in not intended to be put "as is" in your branch, but I hope to have given you some ideas for the future :) There could be bugs, of course, and I'll be glad to hear even a "this is shit", if you care ;)

Thank you!