OS X pathCache bugfix/compatibility + small i18n fix

This mainly fixes the UTF-8 NFC/NFD pathCache bug on OS X by converting the filenames returned by PhysFS from NFD to NFC. It also includes some changes to gl-fun.h and mkxp.pro that make compiling mkxp on OS X easier and less error-prone. The cmake files aren't modified at all, since I really don't know what I'm doing there.

I've also added a small configuration option called iniCodec which will allow the user to specify the character encoding of the Game.ini file. While RGSS uses UTF-8 almost everwhere, Game.ini unfortunately remains Widnows-codepage specific. Like the UTF-8 fix above, it converts the text via iconv. This creates an extra dependency on Windows, so it can be disabled via DISABLE_INI_CODEC with qmake.