Adds ly:define-event-class (issue1867050)

[n . puttock]

Hi Mike,

I don't trust Rietveld not to swallow my comments, so I'm posting a few
at a time just in case it breaks again. :)

Cheers,
Neil


http://codereview.appspot.com/1867050/diff/17001/18001
File input/regression/scheme-text-spanner.ly (right):

http://codereview.appspot.com/1867050/diff/17001/18001#newcode5
input/regression/scheme-text-spanner.ly:5: texidoc = "uses
define-event-class to create a fully functional
A more generic docstring would be better, since you're exercising
several functions useful for implementing spanner engravers.

http://codereview.appspot.com/1867050/diff/17001/18001#newcode61
input/regression/scheme-text-spanner.ly:61: (side-axis . ,Y)
remove this to check `set-axis!' works

http://codereview.appspot.com/1867050/diff/17001/18001#newcode65
input/regression/scheme-text-spanner.ly:65: (Y-offset .
,ly:side-position-interface::y-aligned-side)
remove (same as side-axis)

http://codereview.appspot.com/1867050/diff/17001/18001#newcode111
input/regression/scheme-text-spanner.ly:111: (ly:grob-set-property!
(begin
  (ly:grob-set-property! grob 'side-axis axis)
  (ly:grob-chain-callback ...

http://codereview.appspot.com/1867050/