bug#18739: 24.3; Request for a hook to be provided when scrolling will move the cursor

[Josh]

It would be helpful to have a hook that would be called before any
scrolling command moves the cursor.  In other words, I want to be
notified when an update to the display will force the location of
`point' to change in the current buffer.

One motivation for such a hook is the ability to save the current
cursor location before scrolling so that it is possible to
automatically jump back to that position after scolling.