Add display method for \tweak (fixes issue 1733)

Add display method for \tweak.

* input/regression/display-lily-tests.ly:

  add tests for \tweak

* scm/define-music-display-methods.scm

  (scheme-expr->lily-string): don't funnel booleans through pretty-print
  (EventChord): treat simple_element with 'tweaks list as note_chord_element
                to preserve < > around tweaked note

* scm/display-lily.scm (music->lily-string):

  process 'tweaks via new function music->lily-string

[Neil Puttock, 2011-07-03 21:59:56]

This patch allows \tweak to be displayed properly when using \displayLilyMusic.

* scm/display-lily.scm (music->lily-string):

  process 'tweaks via new function music->lily-string

This should read

  process 'tweaks via new function tweaks->lily-string

[pkx166h, 2011-07-04 00:04:08]

Reg tests pass and no make problems

James

[Carl, 2011-07-05 03:48:46]

LGTM

Carl

[Neil Puttock, 2011-07-07 19:23:04]

On 5 July 2011 04:48,  <Carl.D.Sorensen@gmail.com> wrote:
> LGTM

Thanks, Carl.

Pushed: d5766025a1573c709dfa3c9663c1c6b903abec24