Pass debug and debug-brk flags to node for debugging Tap tests

Adds two new flags to tap to assist with debugging your node Tap tests:

--debug: Pass the '--debug' flag to node for debugging
--debug-brk: Pass the '--debug-brk' flag to node for debugging

e.g.
$ tap --debug-brk test/foo.js
debugger listening on port 5858

You can then fire up node-inspector and debug like a boss.