ly_display_scm is beautiful!

[Graham Percival]

Could some frog, or not-experienced developer, write something about
ly_display_scm() in the CG?  It's mentioned in passing, but not
explicitly.

For example, I'm working on the 1336 segfault, and I've just written/added:

  if (ly_is_procedure (val)
      || is_simple_closure (val))
    {
      Grob *me = ((Grob*)this);
printf("grob-property 188: %p %p ", me, &me->mutable_property_alist_);
printf("~~ \n");
ly_display_scm(sym);
ly_display_scm(val);
printf("~~ \n");
      val = me->try_callback_on_alist (&me->mutable_property_alist_, sym, val);
printf("... done grob-property \n");
    }

to give me more debugging info.  Before I discovered ly_display_scm, I
was looking at pointers and hoping that one of them would be a (nil).
Yes, I know that most people like debuggers, but I prefer printf().

If nobody else does this in the next few days, I'll do it, but I think
this would be a good small step for anybody wanting to "get their feet
wet".

- Graham