Assert: Add alias for throws called 'raises'

Brings back the original method name, for compatibility with environments that consider 'throws' a reserved word.

Fixes #663

Also moves some tests for assert to its own file, in a separate commit. The new raises test is at the end of `test/assert.js`.

The jshint exception is necessary to make it shut up about `assert[ "throws" ]` not using dot notation.