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

[<emacs@kosowsky.org>]

Ted Zlatanov wrote at about 10:53:03 -0500 on Monday, November 11, 2013:
 > On Tue, 05 Nov 2013 18:54:49 -0500 <emacs@kosowsky.org> wrote: 
 > 
 > > Alp Aker wrote at about 18:16:14 -0500 on Tuesday, November 5, 2013:
 > >> > Where is "trunk" located?
 > >> > The latest version in ftp://ftp.gnutls.org/gcrypt/gnutls/w32/ is 3.2.6
 > >> > which still crashes as before...
 > >> 
 > >> He meant emacs trunk:
 > >> 
 > >> bzr://bzr.sv.gnu.org/emacs/trunk
 > 
 > > I'm confused... the patch Ted wants me to test is part of the gnutls
 > > libraries... which at least until now haven't been part of the windows
 > > emacs package...
 > 
 > The patch is against Emacs trunk.  Downloading an Emacs build made after
 > my last commit (November 5 2013 or later) will let you confirm if the
 > fix is good or not.
 > 
 > Thanks
 > Ted

I tested it against the November 6th build.

It seems to work in the sense that now instead of crashing emacs,
gnutls just throws me into the emacs debugger:

Debugger entered--Lisp error: (gnutls-error #<process tls> -64)
  signal(gnutls-error (#<process tls> -64))
  gnutls-negotiate(:process #<process tls> :type gnutls-x509pki
  :hostname "imap.gmail.com")
  open-gnutls-stream("tls" "tls-buffer" "imap.gmail.com" "imaps")
  eval-region(19 83 t #[257 "\300\242b\210\301\207" [(83)
  (open-gnutls-stream "tls" "tls-buffer" "imap.gmail.com" "imaps")] 2
  "\n\n(fn IGNORE)"])  ; Reading at buffer position 83
  eval-defun-2()
  eval-defun(nil)
  call-interactively(eval-defun nil nil)
  command-execute(eval-defun)


Presumably, this error is due to the fact that
"/usr/ssl/certs/ca-bundle.crt" is not a valid file on Cygwin (despite
the comment in gnutls.el implying that it is!)

Of course, it all works fine with the elisp patch that I had
previously submitted.

Note it also works fine in a degenerate way without cygwin-mount since
the mapcar file-exists-p statement returns that none of the files
exists.

So, now that the bug that crashes the emacs process has been fixed,
perhaps it's time to make gnutls-trustfiles actually work under
cygwin.

Indeed, it's worse than just not "working". If cygwin-mount is loaded
then open-gnutls-stream will throw an (incomprehensible) error each
and every time due to the fact that file-exists-p shows the trustfile
exists while the C-code is passed a file path that is not recognized by
the OS. So, there remains a fundamental incompatibility between
cygwin-mount and gnutls.el.