bug#20169: 25.0.50; doc of `posn-actual-col-row'

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

> > Please add the information that is in the doc string to (elisp)
> > `Accessing Mouse'.  This means both the reference information about what
> > happens if POSITION does not contain the actual position and the guide
> > information about using `posn-col-row' in that case.
> 
> The first part is already there, isn't it?

Do you mean this?

  The function returns `nil' if POSITION does not include actual
  position values.

I meant that the manual should include the information that is in
the last two paragraphs of the doc string:

  Return nil if POSITION does not contain the actual position;
  in that case `posn-col-row' can be used to get approximate values.
  POSITION should be a list of the form returned by the `event-start'
  and `event-end' functions.

  This function does not account for the width on display, like the
  number of visual columns taken by a TAB or image.  If you need
  the coordinates of POSITION in character units, you should use
  `posn-col-row', not this function.

This is a lot more (and more useful) information than just what
is in its first line:

  Return nil if POSITION does not contain the actual position;