call lost_leadership callback after append callback (#37)
call lost_leadership callback after append callback (#37)

It makes more sense to have this order because callers
need to be able to clean up any pending appends before
the role changes. It's much harder to do this with the
previous callback order.
Cistern/sacq,Preetam/libab,Cistern/sacq,Preetam/libab,Preetam/libab,Preetam/libab