and define this as the "start of request timestamp".

Define "end of request timestamp" as when we are ready to transmit
HTTP header back.

SHMlog the start and difference between start and stop with ReqServTime
tag.

Keep track of idle sessions using CLOCK_MONOTONIC to avoid trouble
here should our clock get stepped.




git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@583 d4fa192b-c00b-0410-8231-f00ffab90ce4