On Windows, certain characters are prohibited in file names, most
prominently the colon. When fopen() is called with such an invalid file
name, the underlying Windows API actually reports a particular error,
but since there is no suitable errno value, this error is translated
to EINVAL. Detect the case and report ENOENT instead.
Signed-off-by: Johannes Sixt <j6t@kdbg.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>