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

[Stefan Monnier]

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

For the long term maintainability of the code, adding more quirks into
the code for the sake of a few users who can fix their problems easily
is not such a hot idea either.
The key here is "fix ... easily", which can be done by adding code that
detects the problem and warns the user about it.


        Stefan