system-count=1 -> ragged-right=##t

[Graham Percival]

Here's an interesting idea that my brother mentioned while I was
complaining about a related problem in the docs:
- if system-count is 1, enable ragged-right by default.
(If system-count is > 1, leave it disabled)

Obviously if the user specifies ragged-right manually, take that
value instead of looking at the number of systems in the piece.

This would simply the docs (particularly LSR stuff), bug reports,
and the like.  On initial review, I can't see any downside[1].  Joe,
would this be easy to add?  Can you see any downsides to this?

[1] provided that the docs are clear about this and mention that the
user can specify ragged-right manually -- but trust me, I can handle the
doc part of this.  :)

Cheers,
- Graham