added %r to cannot open file, handy for some of my more
weird file servers where you can get some helpfull info
from lower layers, eg
	p: cannot open 'junk' - cifs: server disconnected

-Steve

Reference: /n/sources/patch/applied/better-errmsg
Date: Fri Feb 11 16:11:20 CET 2005

--- /sys/src/cmd/p.c	Fri Feb 11 16:09:32 2005
+++ /sys/src/cmd/p.c	Fri Feb 11 16:09:27 2005
@@ -33,7 +33,7 @@
 			n++;
 			f = open(argv[0], OREAD);
 			if(f < 0){
-				fprint(2, "p: can't open %s\n", argv[0]);
+				fprint(2, "p: can't open %s - %r\n", argv[0]);
 				continue;
 			}
 			printfile(f);