Check for VARNISHSRC in flint.sh

src/flint.sh

@@ -6,6 +6,11 @@ if [ "x$1" = "x-ok" -a -f _.fl ] ; then
 	exit 0
 fi
 
+if [ "x${VARNISHSRC}" = "x" ] ; then
+    echo >&2 VARNISHSRC must be set
+    exit 2
+fi
+
 flexelint \
 	-D__FLEXELINT__ \
 	${VARNISHSRC}/flint.lnt \