Generic issue for CD drag and drop related crashes

[rakslice]

While I have been testing the CD drag and drop feature I have been getting sporadic crashes; I don't think this is just a regression due to kanjitalk755#218

Let's try to reproduce and collect repros for whatever crashes we can around this.
Testing should cover:

• Incorrect use of the drag and drop feature (e.g. dragging without ejecting the existing disc first)
• Use of the feature after a restart within the guest OS

[rakslice]

• Also add an alert of some kind when the user is trying to mount a cd image but they need to do something differently