Don't use net_port as port to connect to

the connect commands supports adding the port with ":"
like "connect 10.1.2.3:27016" - if no port is set, it defaults to 27015

net_port is still used as the port to listen on and to send from.
Add CVar r_displayGLSLCompilerMessages to suppress AMD driver warnings

The AMD drivers output a lot of useless warnings when compiling the shaders.
Those are pretty annoying, especially as idRenderProgManager::LoadGLSLShader
prints out the whole shader with them..
So I added this CVar to suppress them (when it's set to 0)