This fixes#976, fixes#974, fixes#444.
On Windows the standard stream open() functions expect bytes encoded in
current system encoding, not UTF8. Since we're dealing with UTF8
throughout the application this results in wrong paths being passed and
failure to open files. As a solution, we convert the paths to UTF16 via
the WCHAR character type and use the special Windows-specific overloads
of open() functions.
d24f368efe