[PATCH] Support forwarding intercepted but not bumped connections to cache_peers

Hello,

    When talking to a cache_peer (i.e., sending a CONNECT request before
tunneling the transaction), tunnel code is using a clever hack: Squid
does not parse the CONNECT response from peer but blindly forwards it to
the client. This works great and simplifies code a lot, except when the
client connection was intercepted and, hence, the client did not send a
CONNECT request and is not expecting a CONNECT response.

In those situations, the patch accumulates, parses, and strips the peer
CONNECT response (or closes connection on errors).

The existing tunnel I/O code is too simple to accommodate that task --
it cannot accumulate read data (its I/O buffers work in lockstep
fashion, writing everything it reads before reading again). Instead of
rewriting the entire tunnel code to use more complex buffers, I added a
temporary accumulation buffer for the CONNECT response. That buffer is
not allocated unless it is needed and does not grow beyond
SQUID_TCP_SO_RCVBUF size, just like the simple buffers.

Thank you,

Alex.