Bug 672760 - Postponed transaction applied invalid date

Part 2: GDate can represent a wider range that GDateTime, so make
sure that GDates outside of the range are clamped. The GDateTime
range is 1 - 9999 CE, more than wide enough for most purposes. GDate
can represent out to 65535CE, but the significant difference is that
a freshly-cleared GDate is 0CE, which GDateTime won't accept. That we
set to the Unix Epoch 0, 1970-Jan-1.

gnc_sx_incr_temporal_state can invalidate the gdate, so make sure that a
valid date is stored.

Adding the inst->temporal_state ptr to the sx->deferredList is wrong, it's
freed shortly after adding, causing later access to the freed ptr.
Add a clone instead.

src/app-utils/gnc-sx-instance-model.c

@@ -1318,7 +1318,8 @@ gnc_sx_instance_model_effect_change(GncSxInstanceModel *model,
             case SX_INSTANCE_STATE_POSTPONED:
                 if (inst->orig_state != SX_INSTANCE_STATE_POSTPONED)
                 {
-                    gnc_sx_add_defer_instance(instances->sx, inst->temporal_state);
+		     gnc_sx_add_defer_instance(instances->sx,
+					       gnc_sx_clone_temporal_state (inst->temporal_state));
                 }
                 increment_sx_state(inst, &last_occur_date, &instance_count, &remain_occur_count);
                 break;

src/engine/SchedXaction.c

@@ -1151,8 +1151,11 @@ SXTmpStateData*
 gnc_sx_create_temporal_state(const SchedXaction *sx )
 {
     SXTmpStateData *toRet =
-        g_new0( SXTmpStateData, 1 );
-    toRet->last_date       = sx->last_date;
+	 g_new0( SXTmpStateData, 1 );
+    if (g_date_valid (&(sx->last_date)))
+	 toRet->last_date       = sx->last_date;
+    else
+	g_date_set_dmy (&(toRet->last_date), 1, 1, 1970);
     toRet->num_occur_rem   = sx->num_occurances_remain;
     toRet->num_inst   = sx->instance_num;
     return toRet;