[1/5] secur32: Require gnutls for schannel

[Dan Kegel]

> If its easier with gnutls, please use it.

+1

I also agree that nss is likely to replace openssl as the toolkit
of choice. But if depending
on gnutls is the easiest path to a working schannel, that's
the right thing to do.  We can always change later if a
compelling reason arises.
- Dan