[PATCH] HTTP Compliance: Reply with an error if required validation failed

HTTP Compliance: Reply with an error if required validation failed

RFC 2616 says that proxy MUST not use stale entries that have s-maxage,
proxy-revalidate, or must-revalidate cache-directive.

Add new fail_on_validation_err request flag to store result from
refreshCheck(). It is needed to avoid refreshLimits() recalculation in
clientReplyContext::handleIMSReply().

Split LOG_TCP_REFRESH_FAIL into LOG_TCP_REFRESH_FAIL_OLD (stale reply
sent) and LOG_TCP_REFRESH_FAIL_ERR (error forwarded). Though both logged
as TCP_REFRESH_FAIL for backward-compatibility with external scripts, etc.

Co-Advisor test cases:
     test_case/rfc2616/noSrv-hit-must-reval-s-maxage-resp
     test_case/rfc2616/noSrv-hit-must-reval-proxy-revalidate-resp
     test_case/rfc2616/noSrv-hit-must-reval-must-revalidate-resp

-------------

Is it a good idea to log new LOG_TCP_REFRESH_FAIL_OLD (stale reply sent)
and LOG_TCP_REFRESH_FAIL_ERR (error forwarded) as
"LOG_TCP_REFRESH_FAIL"? There are probably a lot of scripts out there
that cannot easily handle new outcomes, but I do not know whether we
should be kept hostage to them as the two outcomes are rather different.
Will we have to use the old tag forever?

Thank you,

Alex.