[frogs] PATCH for getting output-suffix to work (Trackers 714 and 404)

[Ian Hulin <ian@xxxxxxxxxxxx>]

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Hi Carl,

Here's the first stage of work on these trackers,  I've taken the work Marek Klein did and polished it a little bit.
A patch is attached, also some .ly files I used to test it.

I'd like to do a phase 2 to this later to set up a property setting so we can do something like

\book \with {output-suffix = "Gibbon"}
{ music...}
\book \with {output-suffix = "Vole"}
{ music...}
\book \with {output-suffix = "Aardvark"}
{ music...}

or
\book {
output-suffix="Newt"
music...
}
but that's for the future

Cheers,

Ian Hulin