The default is always UTF-8.

Don't define HAVE_FS_CHARSET, and make GetFSCharset() return "ACP"
instead of "UTF-8".  Ignore the configuration setting, which had no
effect anyway.

Use wchar_t for everything on Windows.  Solves a lot of filesystem
charset problems.

Don't use FILE_ATTRIBUTE_NORMAL, it's a "magic" value for something
else.  To check if a file is a regular file, we need to check if it's
NOT a directory (or a device).

Type-safe wrapper for uri_get_suffix().

Eliminate duplicate code.