HTTP Compliance: Support If-Match and If-None-Match requests.

HTTP Compliance: Support If-Match and If-None-Match requests.

Add support for If-Match and If-None-Match headers as described in RFC 2616
(sections 14.24 and 14.26 in particular).

Moved IMS handling from clientReplyContext::cacheHit() to
clientReplyContext::processConditional() while preserving the original IMS
logic, except for the case when a request has both IMS and If-None-Match.

Co-Advisors test cases:
    test_clause/rfc2616/ifMatch-mismatch-strong
    test_clause/rfc2616/ifMatch-mismatch-weak
    test_clause/rfc2616/ifNoneMatch-match-imsNone
    and many more