A couple misc cleanup tasks, mostly around minification

* Internalized TraceKit._has. It was a private method anyways.
* Created an UNKNOWN_FUNCTION constant since '?' was used several times.
* added _isUndefined for a consistent check
* _slightly_ refactored getSource
Oops, debug was used. :)
Merge remote-tracking branch 'mattrobenolt/cleanup'

Conflicts:
	tracekit.js
Merge branch 'master' of https://github.com/occ/TraceKit