Aldrin should not offer to save unchanged files

[user]

When quitting or opening a file, Aldrin always displays the dialog box that asks if you want to save the file.

This is unnecessary and interferes with the work flow in the following circumstances:

* When a file is loaded as the first action after start-up * When a file has not been changed since it was loaded from disk * When qutting Aldrin after having saved the file and not done any changes

The simplest way of doing this would probably be to have a boolean state, set it to clean after startup, loading and saving, and set it to dirty when any other operation is done. This system would of course have to be refined when undo/redo is implemented.