Provide stack traces on doh errors

[Adam Peller]

From Julian Cerruti (IBM):

Here I provide two patches (a 'hackish' easy version - 'hack', and a bit more refined one - 'tidy') that basically modify doh to send Error objects generated inside unit tests to console.error instead of console.debug, if we're running inside Firefox and that method is available.

This adds the stack trace together with the Error object in the Firebug console. Also, the objects in the Firebug console are actionable and can be inspected.

If using dojo, this works specifically well if matched with Firebug 1.5 (b5 or later), which properly jumps to the proper source code file and line when clicking on each method in the stack trace.