bug#27530: patch to cut and copy secondary

[Tak Kunihiro]

>>> In Emacs 24, we have changed how selection works to conform with
>>> other modern X applications, by having primary selection set only
>>> via mouse gestures, whereas keyboard commands work with the
>>> clipboard.  Doesn't your proposal go in the opposite direction?
>>
>>  I see.  I wonder if the direction lets the secondary selection
>> react with region-reacting functions such for comment-dwim.
>
> I'm not sure I understand this comment.  Can you elaborate?

I often want to comment out text with mouse-secondary-overlay.

I meant if `mouse-secondary-overlay -> region' direction is not
supported, text with mouse-secondary-overlay cannot be commented out
until I select the text again as region.  I thought it is good to
avoid redundant operation if possible.

Probably I misunderstand two relationships.
 primary   -- region
 secondary -- mouse-secondary-overlay