bug#25061: consider adding %COMPAT to default gnutls priority string

[Ted Zlatanov]

On Sun, 17 Dec 2017 17:17:41 +0200 Eli Zaretskii <eliz@gnu.org> wrote: 

EZ> Btw, you may wish to consider implementing the removal of %DUMBFW
EZ> inside gnutls.c, when the version of GnuTLS doesn't support that, this
EZ> could be cleaner on the Lisp level.

Emacs now collects all the GnuTLS extensions into the list returned by
`gnutls-available-p' and that's used by gnutls.el. I hope that's enough
to resolve this problem.

I don't think the C code should be modifying the priority string before
it's passed on. That can cause pretty bad problems.

Ted