A few passes included the same list of FF cell types. Make it a global
const instead.
The zinit pass also seems to include a list like that, but given that
it seems to be completely broken at the time (see #1568 discussion),
I'm going to pretend I didn't see that.
o Not all derived methods were marked 'override', but it is a great
feature of C++11 that we should make use of.
o While at it: touched header files got a -*- c++ -*- for emacs to
provide support for that language.
o use YS_OVERRIDE for all override keywords (though we should probably
use the plain keyword going forward now that C++11 is established)