add some debugging output to js tests

- display errors in evaluate / browser code
- capture and display console.log if a test fails (like nose)
fix interrupt test revealed by new output

the shortcut test wasn’t running at all,
due to a ReferenceError.

There was no indication of this fact
because javascript is awesome like that.
Merge pull request #6144 from minrk/show-js-errors

add some debugging output to js tests