The cast operation ignored the cases when the precision and/or the scale exceeded
the limits, 65 and 30 respectively. No errors were reported in these cases.
For some queries this may lead to an assertion abort.

Fixed by throwing errors for such cases.


mysql-test/r/type_newdecimal.result:
  Added a test case for bug #29415.
mysql-test/t/type_newdecimal.test:
  Added a test case for bug #29415.