Testing, systemd support, rfc5188, cleanups

I've pushed up a few patches to github which myself and my colleagues at
YouView have been working on.  I would appreciate a review if possible.

In summary:
 * automated-testing introduces systemd socket activation support and a
   simple automated test framework.
 * rfc5861-control-value-parsing makes polipo recognise
   "stale-while-revalidate" and "stale-if-error" cache-control-flags
 * fix-flags cleans up the naming of the OBJECT_TYPE, OBJECT_FLAG and
   CACHE_CONTROL_FLAG values and fixes a typo in httpTweakCachability

I've only tested these changes on Linux (Fedora 15) as I have no other
development environments available.

You may find that the automated tests fail.  In two of the cases where
I believe that polipo should be caching the requests it doesn't, unless
you kill polipo and re-start it, in which case it will happily serve
from disk cache.  I wonder if this is related to 148f04ff "Tweak
cachability when reading from the disk cache." which I came across while
making the fix-flags changes.

Thanks

Will

------------------------------------------------------------------------------
Write once. Port to many.
Get the SDK and tools to simplify cross-platform app development. Create 
new or port existing apps to sell to consumers worldwide. Explore the 
Intel AppUpSM program developer opportunity. appdeveloper.intel.com/join
http://p.sf.net/sfu/intel-appdev