Ugh, I just realized that a Windows program using a Linux emulation DLL
can probably mix POSIX and WinAPI filesystem calls. So it can open a mix
of POSIX file descriptors (C type: int) and Windows file handles (C
type: HANDLE).

So using `file-handle` in procedure names in a POSIX SRFI is not a good
idea after all.

Is `fd` too short?