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
% new file
applying patch from stdin
% chmod +x
applying patch from stdin
% copy
applying patch from stdin
a
a
% rename
applying patch from stdin
copyx
new
rename
% delete
applying patch from stdin
new
rename
% regular diff
applying patch from stdin
% copy and modify
applying patch from stdin
a
a
b
a
a
% rename and modify
applying patch from stdin
copy2: No such file or directory
a
a
b
c
a