Another write barrier; fix a leak.

Author: jnthn

src/ops/nqp.ops

@@ -783,8 +783,10 @@ Sets an object's serialization context.
 
 */
 inline op nqp_set_sc_for_object(in PMC, in PMC) :base_core {
-    if ($1->vtable->base_type == smo_id)
+    if ($1->vtable->base_type == smo_id) {
         SC_PMC($1) = $2;
+        PARROT_GC_WRITE_BARRIER(interp, $1);
+    }
     else
         Parrot_ex_throw_from_c_args(interp, NULL, EXCEPTION_INVALID_OPERATION,
             "Can only use nqp_set_sc_for_object with a SixModelObject");

src/pmc/stable.pmc

@@ -68,8 +68,16 @@ pmclass STable manual_attrs dynpmc group nqp {
     VTABLE void destroy() {
         /* If a v-table was allocated, free that. */
         STable *st = (STable *)PMC_data(SELF);
-        if (st->vtable)
+        if (st->vtable) {
             mem_sys_free(st->vtable);
+            st->vtable = NULL;
+        }
+        
+        /* If a Parrot v-table mapping was installed, free that. */
+        if (st->parrot_vtable_mapping) {
+            mem_sys_free(st->parrot_vtable_mapping);
+            st->parrot_vtable_mapping = NULL;
+        }
 
         /* Free the underlying struct. */
         mem_sys_free(PMC_data(SELF));