[PATCH] Compliance: delete Warnings that have warning-date different from Date

Compliance: delete Warnings that have warning-date different from Date.

Added HttpReply::removeStaleWarnings() method that iterates over all
Warning headers and removes stale warning-values. If a reply has no
valid Date header, all warning-values with warning-date are removed.
Also, we remove warning-value if we failed to parse warning-date.

removeStaleWarnings() is called from processReplyHeader(), after reply
headers are parsed.

Co-Advisor test cases:
   test_case/rfc2616/date-accept-fmt-warn-asctime-rfc1123
   test_case/rfc2616/date-accept-fmt-warn-asctime-rfc850
   test_case/rfc2616/date-accept-fmt-warn-rfc1123-asctime
   test_case/rfc2616/date-accept-fmt-warn-rfc1123-rfc850
   test_case/rfc2616/date-accept-fmt-warn-rfc850-asctime
   test_case/rfc2616/date-accept-fmt-warn-rfc850-rfc1123