py: Implement long int parsing in int(...).

Addresses issue #627.

py/vm.c

@@ -312,7 +312,7 @@ dispatch_loop:
 
                 ENTRY(MP_BC_LOAD_CONST_INT): {
                     DECODE_QSTR;
-                    PUSH(mp_obj_new_int_from_qstr(qst));
+                    PUSH(mp_load_const_int(qst));
                     DISPATCH();
                 }