test-revert: add revert --all case when nothing changed stable

test-revert: add revert --all case when nothing changed

supposed to succeed without notice

--- a/tests/test-revert.t	Wed Jun 29 16:01:06 2011 -0500
+++ b/tests/test-revert.t	Tue Jun 28 00:56:33 2011 +0200
@@ -12,6 +12,7 @@
   abort: no files or directories specified
   (use --all to revert all files)
   [255]
+  $ hg revert --all
 
   $ echo 123 > b