It is possible to open multiple instances of the about dialog

[Akuli]

While this makes playing with the easter eggs more fun, I think it would be better to allow opening only one about dialog at a time. Plugin manager and settings dialog already disallow multiple instances.

[Moosems]

Maybe by using a message box and giving it a parent? That would be a fairly simple solution, I could get to work on this tomorrow.

[rdbende]

Other dialogs use winfo_exists. The about dialog wouldn't work as a messagebox.