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.

Read the existing assert.throws implementation and its tests, then compare the behavior with the linked Node.js assert.throws documentation. Done means supporting constructor, regular-expression, and validation-function error arguments instead of only instanceof checks, with coverage for each form.

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