Bug #890: Various HTTP workarounds and minor corrections

Bug #890: Various HTTP workarounds and minor corrections

- Automatically time out incorrectly signalled persistent connections
  after 10 seconds of inactitivy. Also gives a warning in cache.log

- New detect_broken_pconn squid.conf option

- Do not strip whitespace from the beginning of HTTP/0.9 replies

- Do not delay forwarding of HTTP/0.9 replies

- Do not delay forwarding of POST/PUT replies. Also includes detection
  of some common forms of abuse of the same for non-HTTP requests.

Forward port of 2.5 patch.