- implement r_noborder, inspired by patch from ensiform (#4289)

- Add Sys_SetEnv for portable setting of environment variables
 - Default ioquake3 to appear on the center of the screen if running in windowed mode.

code/renderer/tr_local.h

@@ -1043,6 +1043,7 @@ extern	cvar_t	*r_showcluster;
 
 extern cvar_t	*r_mode;				// video mode
 extern cvar_t	*r_fullscreen;
+extern cvar_t	*r_noborder;
 extern cvar_t	*r_gamma;
 extern cvar_t	*r_displayRefresh;		// optional display refresh option
 extern cvar_t	*r_ignorehwgamma;		// overrides hardware gamma capabilities