Merge branch 'master' of ssh://jomand@git.sv.gnu.org/srv/git/lilypond

* 'master' of ssh://jomand@git.sv.gnu.org/srv/git/lilypond:
  Update from Jay.
  Updates from Trevor.
  MusicXML: brackets (\startGroup and \stopGroup) need a special engraver add to Staff
  MusicXML: Add possible \layout block, use autoBeaming=##f by default, allow manual beaming
  MusicXML: The <attributes> tag can have multiple <staff-details> children