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

changeset:   0:9c2cf2b35aa7
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     add foo

changeset:   1:3756a9556b89
tag:         tip
user:        test
date:        Mon Jan 12 13:46:41 1970 +0000
summary:     change foo

2 revisions:
9c2cf2b35aa7
3756a9556b89