Add a watch file to help people who build packages themselves look for a new release of varnish

git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@1483 d4fa192b-c00b-0410-8231-f00ffab90ce4

debian/watch

+version=3
+
+# New versions of Varnish are available at SourceForge
+http://sf.net/varnish/varnish-(.*)\.tar\.gz