bug#16475: enhancement request: remove vertical scroll bar automatically when not needed

[Eli Zaretskii]

> Date:  Thu, 26 Oct 2017 09:03:10 -0700
> From:  Keith David Bershatsky <esq@lawlist.com>
> Cc:  16475@debbugs.gnu.org,Martin Rudalics <rudalics@gmx.at>
> 
> The values for window-start and window-end will not necessarily be accurate 
> until somewhere towards the end of redisplay.  A test that relies upon those 
> values to add/remove scroll bars will often fail.

We have the ability to check whether the entire buffer fits in the
window without actually displaying it.  The move_it_to function can be
used for that.