Couch: cache document revs and add "multi" methods
Couch: cache document revs and add "multi" methods

The existing implementation requires making lots of HEAD requests to get
the current document rev.  This patch makes use of an LRUHash to keep
track of revs that have already been seen.  If a rev is in the cache, it
is tried before making a HEAD request.

minad/moneta,minad/moneta