bug#9159: 24.0.50; `undo' is not as good as it should be wrt property changes

[Drew Adams]

> > I already said in the OP that "while correct" (N.B.) "it would be
> > better for the property `foo' to simply be removed."
> 
> I don't think this is a bug (or should be fixed), but I wonder whether
> it would make sense for Fput_text_property to just delete the property
> instead of adding/setting `prop nil' to the property list in general?
> 
> That is, if I say
> (put-text-property (point-min) (1+ (point-min)) 'foo nil)
> 
> today, `foo nil' is added.  Perhaps it should just be ignored if not
> already there, and if it's already set, then it should be removed?
> 
> If we have established that there is no semantic difference 
> between nil properties and missing properties, then this sounds
> like there could be (very minor) memory and redisplay efficiencies
> to be won here.

Presumably Stefan agrees (?) but considers that improvement only cosmetic, so
fodder for the wishlist (/dev/null) cannon.