fix jack_port_rename() detection

libs/backends/jack/wscript

@@ -49,7 +49,7 @@ def configure(conf):
                    uselib = 'JACK')
 
     # Check to see if jack_port_rename() is available and working
-    if Options.options.libjack_link == 'link':
+    if conf.env['libjack_link'] == 'link':
             conf.check_cxx(fragment = "#include <jack/jack.h>\nint main(void) { jack_client_t* c; jack_port_t* p; jack_port_rename (c, p, \"foo\"); return 0; }\n",
                    mandatory = False,
                    execute = False,