internally, with code provided by sslgen.c. All SSL-layer-specific code is
then written in ssluse.c (for OpenSSL) and gtls.c (for GnuTLS).
As far as possible, internals should not need to know what SSL layer that is
in use. Building with GnuTLS currently makes two test cases fail.
TODO.gnutls contains a few known outstanding issues for the GnuTLS support.
GnuTLS support is enabled with configure --with-gnutls
USE_WINDOWS_SSPI on Windows, and then libcurl will be built to use the native
way to do NTLM. SSPI also allows libcurl to pass on the current user and its
password in the request.
