contrib/undumprevlog

--- a/contrib/undumprevlog	Tue Mar 07 12:52:00 2017 -0800
+++ b/contrib/undumprevlog	Thu Mar 02 03:52:36 2017 +0100
@@ -17,7 +17,7 @@
 for fp in (sys.stdin, sys.stdout, sys.stderr):
     util.setbinary(fp)
 
-opener = scmutil.opener('.', False)
+opener = scmutil.vfs('.', False)
 tr = transaction.transaction(sys.stderr.write, opener, {'store': opener},
                              "undump.journal")
 while True: