XSL formatter manages to crash ghini if no institution data is given

[mfrasca]

As a graphical environment, I want computing threads not to mix with the GUI, so that the program doesn't crash.

Expected behaviour

threads computing things should only compute things, not also display messages and dialog boxes. when something goes wrong, they should fail with an error condition (an exception), so that the invoking GUI can display the dialog box.

Opinions

unfortunately, much of bauble/ghini is built around this smart and simple fibra thing, implementing collaborative concurrency, and letting the programmer forget about good behaviour. I think we should really get rid of that.

[mfrasca]

I have added a utils.idle_message function, which you can invoke from any thread.
it should display 'modal' though.

[mfrasca]

it is modal. :-)