merge: remember rename copies and parents properly on commit record copies in dirstate even if rename was remote this lets us record it properly at commit teach checkfilemerge about copies, including merge cases pull old copy code out of commit extend rename-merge1 test to show file index

adding a
diff -r 107ba6f817b5 -r 310ce7989cdc a
--- a/a	Thu Jan 01 00:00:01 1970 +0000
+++ b/a	Thu Jan 01 00:00:02 1970 +0000
@@ -1,2 +1,3 @@ confuse str.splitlines
 confuse str.splitlines
 embedded
newline
+clean diff