test.throws incorrectly implemented

According to http://nodejs.org/docs/v0.4.2/api/assert.html#assert.throws
... assert.throws can be passed three arguments:
`assert.throws(block, [error], [message])`

The `error` parameter can be constructor, regexp or validation function. Nodeunit assumes that `error` is a constructor and simply uses instanceof to validate. This behavior is incorrect. Regexp or validation function should be supported.