Misleading error message about QML Observer

1. Open a Qt Quick UI.
2. Try to debug it on a Qt version which does not have a QML Observer.
   You will see the following error message:
   
   By the way: Shouldn't "Rebuild" be written in quotes?
3. Click "Open Qt4 Options".
   There is no "Rebuild" button. You have to click a Qt version, then "Details" and then a bunch of "Build" buttons appears. "Build", not "Rebuild".

The error message should give correct instructions how to solve the problem.