Regression tests broken

[Neil Puttock]

Hi Reinhold,

I've just encountered the following error while doing make test-baseline:

Reading MusicXML from 04d-Spanners-JScore.xml ...
Converting to LilyPond expressions...
Traceback (most recent call last):
  File "../../../scripts/musicxml2ly.py", line 2625, in <module>
    main()
  File "../../../scripts/musicxml2ly.py", line 2620, in main
    voices = convert (filename, options)
  File "../../../scripts/musicxml2ly.py", line 2530, in convert
    (voices, staff_info) = get_all_voices (parts)
  File "../../../scripts/musicxml2ly.py", line 2256, in get_all_voices
    part_ly_voices[n] = musicxml_voice_to_lily_voice (v)
  File "../../../scripts/musicxml2ly.py", line 2139, in
musicxml_voice_to_lily_voice
    ly_voice = group_tuplets (voice_builder.elements, tuplet_events)
  File "../../../scripts/musicxml2ly.py", line 614, in group_tuplets
    nr = tuplet_elt.number
AttributeError: Tuplet instance has no attribute 'number'

I thought it might be a problem with out of date python files, but
I've done a clean build and it's still broken.

Regards,
Neil