First round of changes for new fmgr interface. fmgr itself and the

First round of changes for new fmgr interface.  fmgr itself and the
key call sites are changed, but most called functions are still oldstyle.
An exception is that the PL managers are updated (so, for example, NULL
handling now behaves as expected in plperl and plpgsql functions).
NOTE initdb is forced due to added column in pg_proc.