[2.9.6] Key signatures are not used

[Christian Hitz]

Hi,

as show in this snipped:

\version "2.9.6"

{ \key aes \major c'' d'' e'' f'' }

version 2.9.6 does not observe key signatures. With the above snipped  
no alterations (sharp, flat or natural) are printed. This still  
worked in 2.9.5.

Christian