Mouse button nomenclature

[John Kodis <kodis gsfc nasa gov>]

There seem to be two different mouse button naming conventions in
use in the Gnome documentation: the "left, middle, right" style, and
the "mouse button 1, 2, 3" style.  In the interest of consistency, I'd
suggest that we pick one style or the other, and use it throughout the
documentation. 

The pros and cons seem to be:

* The "left, middle, right" style:

  - is a bit more concise in most contexts ("right-click" vs "click
    mouse button 1").

* The "mouse button 1, 2, 3" style:

  - applys equally well to both left- and right-handed mouse
    configurations;

  - seems to be used throughout the X documentation;

  - requires less thought (at least for me -- when I read "right mouse
    button", I find myself translating this to "mouse button 3").

-- John Kodis.