[PREVIEW] SMP caching, part3: IPC and shared memory primitives

Hello,

    The attached patch contains the third and last 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 AtomicWordT template description.

However, I do not expect the above items to cause significant changes to
the patch logic, but they are critical to make the code compile on
platforms where we do not yet support SMP caching.

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.