[mms] Add MongoDB cache driver.
Classname may not exist here
[mms] Allow MongoDB to be used as a cache backend.
[mms] Allow MongoDB to be used as a cache backend.
[mms] Fix storing schema information in Horde_Cache.

About 99.9% sure we don't want cached schema information to have a
lifetime of 1 second.  This was resulting in schema queries on every
pageload.  Yikes.