dirstate: fix some problems for recursive case normalization (
issue3342)
file in nested directory causes unexpected abort.
problems below should be fixed for recursive normalization route in
dirstate._normalize():
1. rsplit() may cause unpacking into more than 2 elements.
it should be called with 'maxsplit' argument to unpack
into 'd, f'
2. 'd' is replaced by normalized value prefixed with
'self._root', but this makes 'folded' as absolute path,
and it is unexpected one for caller of recursive
normalization