SBuf merged

Hi all,
  today I merged SBuf into trunk; while we start making use of it,
it's time for the next chunk.
My recommendation would be to merge SBufExtras.* next, as it contains
the CacheMgr integration. This will allow us to measure SBuf's
effectiveness and possibly tune it as we start relying on it.

In order to have the cleanest possible merge path, I ask whoever wants
to review things to check out lp:~squid/squid/stringng (not
-cherrypick as it was done so far). The relevant files are
src/SBufExtras.* (they should probably be renamed, suggestions for a
new name are welcome).

Thanks!

-- 
    /kinkie