Issue 4024: Clarify break-align symbols and space-alist args in IR. (issue 114160044 by address@hidden)

[markpolesky]

Reviewers: ,

Message:
Since no one reviewed this patch, I'm setting its status back to review.
 I'll push it next countdown if I all remains quiet.

Thanks,
Mark

Description:
Things take so long to understand when they're not documented!

Issue 4024 on the tracker:
http://code.google.com/p/lilypond/issues/detail?id=4024

Please review this at https://codereview.appspot.com/114160044/

Affected files (+123, -62 lines):
  M lily/break-alignment-interface.cc
  M scm/define-grob-properties.scm