Here are the Boost-less FGEventMgr updates I promised.
Removed Boost dependencies from FGEventMgr.
Removed Boost configure check.
fgMethodCallback now handles const member functions.
I've successfully tested these changes with gcc and msvc.
radiostack.cxx, fg_init.cxx and main.cxx. If these changes are accepted
then you can remove Time/event.[ch]xx and Include/fg_callback.hxx from
the repository.