Goes back to Body Flags being private

I want to keep Body::Flags and Body::FlagsType away from being used
directly by the user, while still fully supporting operator==. So this
change makes these private again, re-exporting that state through
individual member functions, and uses all of the individual accessor
member functions in the implementation of operator== to avoid regressing
issue #548. This ensures no missing state still in checking for equality
and indeed unit tests pass.