$ hg rename a b
$ hg diff
diff -r b01d46ff402d a
--- a/a Fri Jun 05 15:49:22 2009 +0000
+++ /dev/null Thu Jan 01 00:00:00 1970 +0000
@@ -1,1 +0,0 @@
-a
diff -r b01d46ff402d b
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/b Fri Jun 05 15:49:23 2009 +0000
@@ -0,0 +1,1 @@
+a