Re: line-move-ignore-invisible and global-disable-point-adjustment

[martin rudalics]

> There has not been any compelling evidence that users would ever want to
> set both of those to nil or both to t, other than by accident, so by
> removing those 2 cases we get to eliminate some bugs and also we get to
> avoid having to figure what actually *means* a combination such as "nil
> and nil" or "t and t".

We could finally concentrate on finding the "real" bugs here.

> If we agree that this is a good change, then comes the second part of
> the discussion which is about how to go about doing it: since the value
> of the those vars should be the negative of the other, we can't just use
> defvaralias, so we'll have to declare line-move-ignore-invisible as
> obsolete but still make it work (more or less) as before.

Give `line-move-ignore-invisible' the initial value `undecided', replace
all occurrences where `line-move-ignore-invisible' is set in current
Emacs by a corresponding setting of `global-disable-point-adjustment',
leave a note in the doc-string of `line-move-ignore-invisible' that this
variable is considered obsolete, and change the manual accordingly.

Now the code in `line-move-1' would do the same thing as usual for
`line-move-ignore-invisible' iff the value of this is _nil_, that is,
someone has explicitly set it despite of the obsolescence warning.  If
it's t and `global-disable-point-adjustment' is t too, the latter would
prevail.