bug#15375: 24.3.50; Elisp manual: mention what units are used for window margin functions

[Drew Adams <drew.adams@oracle.com>]

> I left it open to allow you to review the changes.  You can do that
> either by pointing your browser at
> http://bzr.savannah.gnu.org/lh/emacs/trunk/annotate/head:/doc/lispref/displa
> y.texi and going down to line 4160, or by waiting for the next binary
> snapshot of the trunk.

Thanks, and thanks for that URL & line #.

Looks good, but I have these minor suggestions, if you have the time:

1. Move the "(a.k.a.@: ``column'')" to the first occurrence of "character
cell".  I, for one, did not know the latter term, and wondered about it
until I got to that aka.

2. You can remove this part, as it is implied: "; if none of the two margins
exist, the function returns @code{(nil)}."  (It does not hurt, but in that
case please change "none" to "neither", to be clearer.)

3. You should add a comma before "and" in "The argument @var{left} controls
the left margin and @var{right} controls the right margin (default @code{0})."
               ,
Alternatively, you can use ";" instead of ", and", or split it into two
sentences.