default FretBoards context - vertical alignment changed

[Robin Bannister]

>
This can be seen in NR B.3, but the C/F/G snippet (sourcefileline 782) 
in NR 2.4.1. / Predefined fret diagrams is suitable for regression testing.

Starting with doc tarball version 2.12.1-2 the C/F/G diagrams have 
neither their fingering nor their first frets aligned. 
It is as if there were a (private) vertical alignment, which has 
changed from #DOWN to #CENTER. 

See also
http://lists.gnu.org/archive/html/lilypond-user/2009-02/msg00130.html

Cheers,
Robin