[PREVIEW] SMP caching, part1: Core changes and addition of shared memory cache

Hello,

    The attached patch contains the first part of the SMP caching
changes described in the "SMP Rock Store and shared memory cache
patches" email. I labeled it [PREVIEW] because of the following
outstanding TODO items:

 * Portability tests and changes (via Hudson).
 * Add mem_cache shared=on|off parameter.

However, I do not expect the above items to cause significant changes to
the patch.

The patch preamble contains a detailed change log.

For the complete set of changes (all three parts), and for testing,
please see the following Launchpad branch:
  lp:~measurement-factory/squid/3p2-rock

Thank you,

Alex.