Make Xsub printable under flag r +

Reference: /n/sources/patch/applied/rc-pxsub
Date: Wed Dec  7 16:18:34 CET 2011
Signed-off-by: yarikos@gmail.com

--- /sys/src/cmd/rc/pfnc.c	Wed Dec  7 16:13:29 2011
+++ /sys/src/cmd/rc/pfnc.c	Wed Dec  7 16:13:26 2011
@@ -50,6 +50,7 @@
 	Xsimple, "Xsimple",
 	Xrdfn, "Xrdfn",
 	Xqdol, "Xqdol",
+	Xsub, "Xsub",
 0};
 
 void