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