make -werror work on OSX again .. check for daemon only if it isn't OSX as well as rename the function to varnish_daemon not to clash with the OSX daemon definition, tested on linux and osx

git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@4112 d4fa192b-c00b-0410-8231-f00ffab90ce4