Fixed spot where SDL was assuming that two displays having the same origin means they're the same display. Changed it to check for the same extents instead.

(Sam actually wrote this, I'm just reviewing and checking it in.)

src/video/x11/SDL_x11modes.c

@@ -552,7 +552,8 @@ X11_InitModes(_THIS)
                    in all cases.  Anybody want to give this some love?
                  */
                 crtc = X11_XRRGetCrtcInfo(data->display, res, output_info->crtc);
-                if (!crtc || crtc->x != displaydata->x || crtc->y != displaydata->y) {
+                if (!crtc || crtc->x != displaydata->x || crtc->y != displaydata->y ||
+                    crtc->width != mode.w || crtc->height != mode.h) {
                     X11_XRRFreeOutputInfo(output_info);
                     X11_XRRFreeCrtcInfo(crtc);
                     continue;