Using [line-width] with [quote]

[Neil Puttock]

Hi everybody,

This combination is disabled in lilypond-book, but there are several
places in the docs where it's used, resulting in no quote block.

I've just reworked a snippet in the Glossary which would benefit from
this; it's currently a bit too long for the pdf output (the final
snippet here: 
http://kainhofer.com/~lilypond/Documentation/user/music-glossary/clef.html#clef).
 Though it doesn't run off the right hand side, there's an ugly
vertical bar in the right margin.

Regards,
Neil