try #2 to implement what we discussed with Francois and Ruth w.r.t. to error notifications:

- never open the message console automatically, it's just to annoying and very slow when there are many errors
- indicate that there's been an error in the status bar
- make it easy to show/hide the messages by a single clic on the status bar
- report the first (not the last) error in the status bar if the messages are not shown

Feedback is welcome... (We can always revert to the old way if necessary ;-)