Check correct glX extension name for swap_control, but it doesn't look like

 we ever actually look up the symbol...that's probably a bug.  :/

--HG--
branch : SDL-1.2
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/branches/SDL-1.2%402312

src/video/x11/SDL_x11gl.c

@@ -269,7 +269,7 @@ int X11_GL_CreateContext(_THIS)
 	}
 	gl_active = 1;
 
-	if ( !glXExtensionSupported(this, "SGI_swap_control") ) {
+	if ( !glXExtensionSupported(this, "GLX_SGI_swap_control") ) {
 		this->gl_data->glXSwapIntervalSGI = NULL;
 	}
 	if ( !glXExtensionSupported(this, "GLX_MESA_swap_control") ) {