bug#5026: 23.1; add-hook buffer local vs single func

[Kevin Ryde]

Stefan Monnier <monnier@iro.umontreal.ca> writes:
>
> It has various misfeatures.

Such as?  Surely a single function is unambiguous, and needs only a
little care from run-hooks and friends to remain compatible.

(A little care of course always being better than sending thousands of
people for a ride on the rolling-incompatibility treadmill!)