Fix test breakage introduced in 07faba78cf5a

tests/test-diff-unified

@@ -53,6 +53,6 b' rm a'
 echo b > a
 echo a >> a
 echo c >> a
-hg diff -U0 -p
+hg diff -U0 -p --nodates
 
 exit 0

tests/test-diff-unified.out

@@ -50,8 +50,8 b' abort: diff context lines count must be '
 % test off-by-one error with diff -p
 adding a
 diff -r cb9a9f314b8b a
---- a/a	Thu Jan 01 00:00:00 1970 +0000
-+++ b/a	Thu Nov 27 17:46:15 2008 +0000
+--- a/a
++++ b/a
 @@ -1,0 +1,1 @@
 +b
 @@ -2,0 +3,1 @@ a