keeping files (previously) in input/

[Graham Percival]

A few months ago, I removed all non-regression files from input/.
I saved typography-demo.ly and put it in input/regression/, since
this file (apparently) tests all output features.

Are there any other files that would be useful for developers,
that I should rescue?

I've had a quick glance, and the only contenders I see are:
- claop.py: it has a problematic license, but I suppose we could
  automatically run this and generate the score, as a "stress
  test" regtest.  OTOH, if we actually want to do such tests,
  I'm sure that we could write our own python program that
  generates a huge ly file, thereby avoiding copyright problems.

- paddy.abc: might be useful for the new abc2ly regtests?

- puer-fragment.ly: demonstrates (according to the comment) broken
  ligatures in lilypond?

- wilhelm.ly: does some funky spacing stuff


Remember, this discussion is about whether or not these files
should be restored as part of the developer-only regtests.  We've
already decided that they're not worth being added to the Examples
or Snippets.

Cheers,
- Graham