Upgrade blindly to latest LilyPond syntax (again).

No errors this time, but remember that I still haven't tried to
understand or fix any of the conversion errors from a few commits
ago.

$ convert-ly -e student-piece-1.ly
convert-ly (GNU LilyPond) 2.18.0

convert-ly: Processing `student-piece-1.ly'...
Applying conversion: 2.17.0, 2.17.4, 2.17.5, 2.17.6, 2.17.11, 2.17.14, 2.17.15, 2.17.18, 2.17.19, 2.17.20, 2.17.25, 2.17.27, 2.17.29, 2.17.97
Regenerate MIDI+PDF blindly after syntax upgrade.

$ lilypond student-piece-1.ly
GNU LilyPond 2.18.0
Processing `student-piece-1.ly'
Parsing...
Interpreting music...
warning: cannot find property type-check for `forced-distance' (backend-type?).  perhaps a typing error?
warning: skipping assignment
[8][16][24][32][40]
Preprocessing graphical objects...
Interpreting music...
programming error: Impossible or ambiguous (de)crescendo in MIDI.
continuing, cross fingers
programming error: Impossible or ambiguous (de)crescendo in MIDI.
continuing, cross fingers
programming error: Impossible or ambiguous (de)crescendo in MIDI.
continuing, cross fingers
programming error: Impossible or ambiguous (de)crescendo in MIDI.
continuing, cross fingers
MIDI output to `student-piece-1.midi'...
Finding the ideal number of pages...
Fitting music on 3 or 4 pages...
Drawing systems...
Layout output to `student-piece-1.ps'...
Converting to `./student-piece-1.pdf'...
Success: compilation successfully completed