Author: Francesco Chemolli <kinkie@squid-cache.org>

Merge Cache Manager Update branch

Overall view of the changes:
 - cachemanager is now a singleton
 - list of actions is now a Vector (still not ideal, but at least it
 preserves layering)
 - added object-based action management interface to cachemgr.
 old-style c interface is still available (via method overload)
 - cachemgr initialization functions have been moved to each modules'
 Init call or (where applicable) constructor. This has the effect of
 reducing each module's interface, and to get rid of some module
 frameworks' extra initialization work
 - fixed tests to work with the new framewor (including the creation of
 a small stub in tests/)
 - added some documentation

What I left off is:
 - change the actionslist from a Vector to a sorted linked-list (need
 the generic linked-list class first)