Fix pipelining.

A braino in http_Dissect() resulted in an off-by-one error
(protected with assert now)

Move any remaning bytes in buffer to front and check for
a complete header before arming the eventloop on the
session.



git-svn-id: http://www.varnish-cache.org/svn/trunk@302 d4fa192b-c00b-0410-8231-f00ffab90ce4