fix output of test-backout.

fix output of test-backout.

--- a/tests/test-backout.out	Thu Aug 03 15:12:15 2006 -0700
+++ b/tests/test-backout.out	Fri Aug 04 10:37:40 2006 -0700
@@ -27,7 +27,7 @@
 reverting a
 changeset 3:4cbb1e70196a backs out changeset 1:22bca4c721e5
 the backout changeset is a new head - do not forget to merge
-(use "backout -m" if you want to auto-merge)
+(use "backout --merge" if you want to auto-merge)
 b: No such file or directory
 adding a
 adding b