'bach accidental style

[Simon Albrecht]

Hello,

I would like to have a custom accidental style acting like manuscripts 
and first editions of Seb. Bach do:
– do not remember accidentals*
– unless a pitch is immediately repeated
– or with chromatic steps: an accidental should always be printed if the 
previous note has the same pitch, but a different alteration.
I find the mechanism for defining accidental styles difficult (see 
<http://lists.gnu.org/archive/html/lilypond-user/2014-02/msg00250.html>); can 
anyone help with this? It might be a modification of 'forget.

Yours, Simon

* except of course those in the key signature