Widgets: Do not draw a scroll bar where none is needed

[tomreyn]

Many windows, usually prompt / dialog windows, have scroll bars, but all of their content is always visible and there is no way to scroll in them. Other prompt / dialog windows do not have scroll bars. No scroll bars should be drawn / displayed where none are needed.

Examples where windows have superfluous scroll bars:
* Error: Some network slots are still unconnected.
* Exit Game?: You win!, Exit Game?
* Exit Game?: Exit Game?
* Exit Program?: Exit Program?