Reenable xbios usage to get relative mouse motion

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%402080

src/video/gem/SDL_gemvideo.c

@@ -203,9 +203,9 @@ GEM_CreateDevice(int devindex)
     if (!(device->hidden->use_dev_mouse)) {
         vectors_mask |= ATARI_XBIOS_MOUSEEVENTS;        /* XBIOS mouse events */
     }
-    if (Getcookie(C_MiNT, &dummy) == C_FOUND) {
+    /*if (Getcookie(C_MiNT, &dummy) == C_FOUND) {
         vectors_mask = 0;
-    }
+    }*/
 
     SDL_AtariXbios_InstallVectors(vectors_mask);