Fix to bug 25504 for gnutls based schannel

[Hans Leidekker]

On Mon, 2011-04-18 at 04:23 -0500, Ken Thomases wrote:
> >> I also wonder why libgcrypt is now needed, where this dll is using libgnutls?
> > 
> > Yes, if there's a way to set the locking functions via gnutls then we
> > wouldn't need to load libgcrypt.
> 
> http://www.gnu.org/software/gnutls/manual/gnutls.html#Multi_002dthreaded-applications
> 
> Apparently, one uses gnutls_global_set_mutex() to configure the locking functions used by GnuTLS.

Yes, that seems to do what we need, but it must be a recent addition
because it's missing here from libgnutls.so.26.14.12.