Allow exchanging nodes with oparity_dynamic and delete their in-array.

[r19035]

ir/ir/irgmod.c

@@ -96,8 +96,6 @@ void exchange(ir_node *old, ir_node *nw) {
 		/* Else, do it the old-fashioned way. */
 		ir_node *block;
 
-		assert(get_irn_op(old)->opar != oparity_dynamic);
-
 		hook_turn_into_id(old);
 
 		block = old->in[0];
@@ -109,6 +107,10 @@ void exchange(ir_node *old, ir_node *nw) {
 			}
 		}
 
+		if (get_irn_op(old)->opar == oparity_dynamic) {
+			DEL_ARR_F(get_irn_in(old));
+		}
+
 		old->op    = op_Id;
 		old->in    = NEW_ARR_D (ir_node *, irg->obst, 2);
 		old->in[0] = block;