Fix crashes in test-engine on Arch Linux.

Root cause is mutating a list while it's iterating. We're able to
protect it in two cases, have to copy it in xaccTransScrubGainsDate.

libgnucash/engine/Account.cpp

@@ -1342,6 +1342,12 @@ xaccFreeAccount (Account *acc)
     priv = GET_PRIVATE(acc);
     qof_event_gen (&acc->inst, QOF_EVENT_DESTROY, NULL);
 
+    /* Otherwise the lists below get munged while we're iterating
+     * them, possibly crashing.
+     */
+    if (!qof_instance_get_destroying (acc))
+            qof_instance_set_destroying(acc, TRUE);
+
     if (priv->children)
     {
         PERR (" instead of calling xaccFreeAccount(), please call\n"

libgnucash/engine/Transaction.c

@@ -2924,7 +2924,8 @@ static void
 xaccTransScrubGainsDate (Transaction *trans)
 {
     SplitList *node;
-    for (node = trans->splits; node; node = node->next)
+    SplitList *splits_copy = g_list_copy(trans->splits);
+    for (node = splits_copy; node; node = node->next)
     {
         Split *s = node->data;
 
@@ -2943,6 +2944,7 @@ xaccTransScrubGainsDate (Transaction *trans)
             FOR_EACH_SPLIT(trans, s->gains &= ~GAINS_STATUS_DATE_DIRTY);
         }
     }
+    g_list_free(splits_copy);
 }
 
 /* ============================================================== */

libgnucash/engine/test/utest-Transaction.cpp

@@ -1427,6 +1427,9 @@ test_do_destroy (GainsFixture *fixture, gconstpointer pData)
     g_object_ref (base->txn);
     g_object_ref (fixture->gains_txn);
 
+   /* Protect against recursive calls to do_destroy from xaccTransCommitEdit */
+    xaccTransBeginEdit(base->txn);
+
     base->func->do_destroy (base->txn);
     g_assert_cmpint (test_signal_return_hits (sig), ==, 1);
     g_assert (base->txn->description == NULL);