Update Bach BWV 988 var27

Bar 25: g->gis on 1st note of bass, tied to last gis from bar 24
(Steve Shorter)
Bar 28: treble clef, last d, add tie to first d from bar 29
Add fermatas to closing bar
Update to Lilypond v2.16.1
(Javier Ruiz-Alma)
Close #54