bug#15648: 24.2.50; gnutls SSL connection to IMAP server causes emacs to crash completely

[Stefan Monnier <monnier@IRO.UMontreal.CA>]

> Would any C-facing code, then, need to apply this function before
> passing a filename to the OS?

I guess so.  I'm much too soaked in the POSIX world where this new
function would default to being a nop, to have a good idea of exactly
where/when this would be needed.

My first idea, w.r.t cygwin-mount was that it should operate "at the
boundary" where we receive filenames from outside, such as in
substitute-in-file-name and when processing command line arguments.

But if we want cygwin names to work on variables set via Elisp
customization, that means it would have to operate at a much
lower level, so maybe "any C-facing code" is the right place, indeed.

But it should probably be "C-facing code except for the code in
file-handlers", since presumably those would already be handled by the
magic-file-handler so by the time we get to the default code there's no
need for any translation.

IOW it should be "any C-facing code which uses files but can't be passed
through the magic file handler".  Of course, it can also be used by
Elisp code when passing file names to external processes.


        Stefan