app: rename compat parasite s/gimp-compatibility-mode/gimp-xcf-foo/

Not sure why, ask Mitch! :-)

app/xcf/xcf-load.c

@@ -365,7 +365,7 @@ xcf_load_image (Gimp     *gimp,
 
   /* check for a gimp-compatibility-mode parasite */
   parasite = gimp_image_parasite_find (GIMP_IMAGE (image),
-                                       "gimp-compatibility-mode");
+                                       "gimp-xcf-foo");
   if (parasite)
     {
       GimpImagePrivate *private = GIMP_IMAGE_GET_PRIVATE (image);

app/xcf/xcf-save.c

@@ -418,7 +418,7 @@ xcf_save_image_props (XcfInfo    *info,
       /* Save the GIMP version we are trying to get compatible with.
        * This specific information is unused as of now though. */
       gimp_image_get_xcf_version (image, FALSE, &gimp_version, NULL);
-      compat_parasite = gimp_parasite_new ("gimp-compatibility-mode",
+      compat_parasite = gimp_parasite_new ("gimp-xcf-foo",
                                            GIMP_PARASITE_PERSISTENT,
                                            sizeof (gimp_version),
                                            &gimp_version);