Add a GNUTLS knob (off by default for now) that controls our use of the
GNU Transport Layer Security library, aka the security/gnutls port.
Before 2009-09-26/revision 1.311 we had used this opportunistically,
then it was disabled across the board to guarantee consistent builds
and packages, and now it's a proper option that is needed for the game
of Warcraft III and possibly others.
Submitted by: Jan Henrik Sylvester <email@example.com>
Adjusted by: gerald
Feature safe: yes