merge: check filename case collision between changesets for branch merging this patch makes branch merging abort when merged changesets have same file in different case on case insensitive filesystem. this patch does not prevent linear update which merges between target and working contexts, because 'branchmerge' is False in such case.

i18n: use encoding.lower/upper for encoding aware case folding this patch uses encoding.lower/upper for case folding, because ones of str can not fold case of non ascii characters correctly. to avoid cyclic dependency and to encapsulate logic of normcase in each platforms, this patch introduces encodinglower/encodingupper in both posix/windows specific files. this patch does not change implementation of normcase() in posix.py, because we do not know the encoding of filenames on POSIX. some "normcase()" are excluded from function wrap list in hgext/win32mbcs.py, because they become encoding aware by this patch.