[merge request] Minor bugfixes and docs.

[Teika Kazura <teika lavabit com>]

Hi. Please merge my branch. It has:

* Bugfix of 'cycle-among-groups'. Some windows were skipped, but
  it's fixed. (Well, no one else has reported it, so I may be
  its only user.)
* `focus-ignore-pointer-events' was a defcustom, but it's for internal
  use, so turned to a defvar. It disposes of an unnecessary item from
  the configurator. I don't think anyone is affected, because even
  if you set it, it soon gets overriden by window cycling.
* Minor doc.

Regards,
Teika (Teika kazura)