fix some failing tests.

src/kernel/region.c

@@ -918,6 +918,8 @@ void free_region(region * r)
         unit *u = r->units;
         r->units = u->next;
         uunhash(u);
+        u->region = NULL;
+        u_setfaction(u, NULL);
         free_unit(u);
         free(u);
     }

src/kernel/unit.c

@@ -749,6 +749,7 @@ void free_units(void)
     while (deleted_units) {
         unit *u = deleted_units;
         deleted_units = deleted_units->next;
+        u_setfaction(u, NULL);
         free_unit(u);
         free(u);
     }