Add a usage string for the standard VSL options.

git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@1010 d4fa192b-c00b-0410-8231-f00ffab90ce4

include/varnishapi.h

@@ -16,6 +16,7 @@ typedef int vsl_handler(void *priv, unsigned tag, unsigned fd, unsigned len, uns
 #define VSL_S_CLIENT	(1 << 0)
 #define VSL_S_BACKEND	(1 << 1)
 #define VSL_ARGS	"bcdr:i:x:CI:X:"
+#define VSL_USAGE	"[-bcCd] [-r file] [-i tag] [-x tag] [-I regexp] [-X regexp]"
 vsl_handler VSL_H_Print;
 struct VSL_data;
 struct VSL_data *VSL_New(void);