Move and isolate cross reference stuff to it's own source file
(vcc_xref.c) and use vcc_ prefix as originally intended.

Also warn about multiple definitions of objects.



git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@1291 d4fa192b-c00b-0410-8231-f00ffab90ce4