Toast all the system-table columns that seem to need it. It turns out

that giving pg_proc a toast table required solving the same problems
we'd have to solve for pg_class --- pg_proc is one of the relations
that gets bootstrapped in relcache.c.  Solution is to go back at the
end of initialization and read in the *real* pg_class row to replace
the phony entry created by formrdesc().  This should work as long as
there's no need to touch any toasted values during initialization,
which seems a reasonable assumption.
Although I did not add a toast-table for every single system table
with a varlena attribute, I believe that it would work to just do
ALTER TABLE pg_class CREATE TOAST TABLE.  So anyone who's really
intent on having several thousand ACL entries for a rel could do it.
NOTE: I didn't force initdb, but you must do one to see the effects
of this patch.