Message-generating tools only work if last statement in codeblock

[ErikBjare]

It tried to do something like:

screenshot()
view_image()

But it never took the screenshot, because the generator wasn't run, and had nowhere to emit messages.

See also #186

[ErikBjare]

Should probably just get rid of the Message-generator tools altogether and simply print to communicate results. Would still need a special solution for the view_image() tool (or just rely on the assumption that it will almost always be the last statement).

Started doing the former in 65bdb8a