win32mbcs: add reversing wrapper for some unicode-incompatible functions.
This changeset fix the problem to use win32mbcs with mercurial 2.3 or
later.
The problem is brought by side effect of modification of
encoding.upper() (changeset 17236:9fb8312dbdbd) because upper() does
not accept unicode string argument. So wrapped util.normcase() which
uses upper() will fail. In other words, upper() and lower() are
unicode incompatible.
To fix this issue, this changeset adds new wrapper for reversed
conversion (unicode to str) for lower() and upper() to use them
safely.