[PATCH 4/8] reconfiguration leaks: Cache Manager menu items

Do not register the same Cache Manager action more than once, to avoid
wrong mgr:menu output and the impression of a reconfigure memory leak.

The old code was comparing action object pointers, which could not work,
and was adding the same action on every reconfigure call for modules
that register with Cache Manager during [re]configuration.

We already have a working method for finding registered actions. Use it.

Alex.