diff: don't crash when merged-in addition is copied Similar to what was explained in the previous commit, the diff code expected copy source to be in "ctx1", which is not always the case during a merge. This has been broken since before hg 2.0. Also similar to the previous commit, we fix the problem by fixing up the copy dict.

--- a/tests/test-diffdir.t	Thu Jan 14 10:14:24 2016 -0800
+++ b/tests/test-diffdir.t	Thu Jan 14 10:22:55 2016 -0800
@@ -68,3 +68,10 @@
   +++ b/a2
   @@ -0,0 +1,1 @@
   +foo
+  $ hg diff --nodates --git
+  diff --git a/a2 b/a2
+  new file mode 100644
+  --- /dev/null
+  +++ b/a2
+  @@ -0,0 +1,1 @@
+  +foo