[MERGE] Closing branch cachemgr-refactoring

Hi all,
  I'm now satisfied with the work done in the cachemgr-refactoring
branch and I propose merging it into squid-3 trunk.

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

While the work is not 100% complete, it's in a state where I'm quite
comfortable merging it in.
The branch is available at lp:~kinkie/squid/cachemgr-refactor/ (see
https://code.launchpad.net/~kinkie/squid/cachemgr-refactor)

What I left off is:
- change the actionslist from a Vector to a sorted linked-list (need
the generic linked-list class first)
- refactor more action registrations to OO interface (IMO it's better
done in the context of each module's development)

Please review, and if it's OK, merge.

-- 
 /kinkie