add sanity check that the saved operations make sense

We had the problem that the maintenance tool can not read the written operations. In this state the installer can not uninstall any component.

And because an update of a component is just uninstall and install in one go also updating does not work correctly.

You see this problem when the update has renamed or moved files.

We had this problem when we updated QtCreator from 3.1.1 -> 3.2 where they moved some plugins around and QtCreator crashes because it just loads the plugins recursively.

My suggestion is to write the operations into a file in temp then read it with the usual installer mechanisms and only if these read values are valid (making thense) write this to the current installer.

Not completly sure what will happen if they are invalid. Maybe a messagebox with corrupted installation and please create a bugreport with the logs.

This suggestion is just an idea to find the real cause, which was not easy to reproduce for me.