Key signature change with naturals before bar line.

[Lasse Rempe]

This question concerns changing the key signature e.g. from a major to a 
flat major. Lilypond standard behavior seems to be printing the natural 
signs and the flat signs both after the bar line, but I have also come 
across the natural signss being noted _before_ the bar line, and the new 
key signature applied _after_ the bar line, see the attached image. 
(Whether this is sensible is another question.) How would I obtain this 
behavior in Lilypond?

I apologize if this is already documented somewhere; a quick search did 
not seem to reveal a solution.

Many thanks,

Lasse