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

[Stefan Monnier <monnier@iro.umontreal.ca>]

I propose to remove line-move-ignore-invisible and make line-move use
(not global-disable-point-adjustment) instead.

It is difficult to get line-move working correctly.  Recently there have
been bugs that only appeared for some combinations of
line-move-ignore-invisible and global-disable-point-adjustment, more
specifically for the case where both were nil.

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".

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.


        Stefan