bug#7236: 24.0.50; make-local-hook missing

[Drew Adams]

> > In Emacs 20 also there is a LOCAL optional arg to add-hook.
> 
> Yes, but its semantics is slightly different: it means "put it on the
> local part of the hook, but only if that local part exists".  
> I.e. it's only effective if make-local-hook has been called before.
> I changed this in Emacs-21 (it an incompatible change, but 
> didn't cause any bug report AFAIR) which made make-local-hook a NOP.
> 
> > Should all code for Emacs 20-24 remove make-local-hook calls and
> > instead add `t' to an existing call to add-hook?
> 
> No. If the LOCAL arg is nil, add-hook will only affect the global part
> of the hook, regardless of whether make-local-hook has been called.

Glad I asked!  I removed calls to make-local-hook yesterday, but put them back
today in code that needs to work in Emacs 20.  Thanks for the explanation.  I
see that you mentioned it in NEWS.21.