Make ConsoleTranscript actually print

ConsoleTranscript used to try and print an undefined variable (string)
to the browser's console, instead of the object sent via the 'show:'
message.
Wrap Javascript objects before showing

Nicolas reminded me that JS objects can't respond to __asString(), and
so must be wrapped. This is done via _st(), which will wrap the object
in a JSObjectProxy. Initial tests seem to indicate that this is enough -
I was able to print the Window object and some other JS objects.
Test printing a JS object that exists everywhere

I don't have access to the `window` object when running Amber on Node,
and probably in other places. The `console` object seems to be pretty
universal.
Merge pull request #487 from kpullen/fixing-up-transcript

Make ConsoleTranscript actually print