In general the "be liberal in what you accept" is a good thing, but
I am not going to be liberal about anything that could cause us to
return wrong content.

The truly consistent thing to do would be to error the fetch, but that
is a bit on the harsh-side for this specific cornercase, so I have
added a test to ignore the first character of the vary header, if it
is a colon.

Fixes:	#763



git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@5334 d4fa192b-c00b-0410-8231-f00ffab90ce4