- Add support for linearly desaturating images via r_greyscale

- Use correct luminance values for rendering textures
Patch submitted by Forrest Voight.

code/renderer/tr_init.c

@@ -920,6 +920,7 @@ void R_Register( void )
 	r_stereoEnabled = ri.Cvar_Get( "r_stereoEnabled", "0", CVAR_ARCHIVE | CVAR_LATCH);
 	r_ignoreFastPath = ri.Cvar_Get( "r_ignoreFastPath", "1", CVAR_ARCHIVE | CVAR_LATCH );
 	r_greyscale = ri.Cvar_Get("r_greyscale", "0", CVAR_ARCHIVE | CVAR_LATCH);
+	ri.Cvar_CheckRange(r_greyscale, 0, 1, qfalse);
 
 	//
 	// temporary latched variables that can only change over a restart