venti: import changes from plan 9

R=rsc
CC=plan9port.codebot
http://codereview.appspot.com/5325044
diff --git a/src/cmd/venti/mkfile b/src/cmd/venti/mkfile
index b5cfff7..d49a5d3 100644
--- a/src/cmd/venti/mkfile
+++ b/src/cmd/venti/mkfile
@@ -5,6 +5,7 @@
 TARG=\
 	copy\
 	read\
+	ro\
 	sync\
 	write\
 	dump\