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.
function is found in prosrc field of pg_proc, not proname. This allows
multiple aliases of a built-in to all be implemented as direct builtins,
without needing a level of indirection through an SQL function. Replace
existing SQL alias functions with builtin entries accordingly.
Save a few K by not storing string names of builtin functions in fmgr's
internal table (if you really want 'em, get 'em from pg_proc...).
Update opr_sanity with a few more cross-checks.
