Set up GnuTLS support.

Set up GnuTLS support.

* configure.in: Set up GnuTLS.

* lisp/net/gnutls.el: GnuTLS glue code to set up a connection.

* src/Makefile.in (LIBGNUTLS_LIBS, LIBGNUTLS_CFLAGS, ALL_CFLAGS)
(obj, LIBES): Set up GnuTLS support.

* src/config.in: Set up GnuTLS support.

* src/emacs.c: Set up GnuTLS support and call syms_of_gnutls.

* src/gnutls.c: The source code for GnuTLS support in Emacs.

* src/gnutls.h: The GnuTLS glue for Emacs, macros and enums.

* src/process.c (make_process, Fstart_process)
(read_process_output, send_process): Set up GnuTLS support for
process input/output file descriptors.

* src/process.h: Set up GnuTLS support.