Clearly state how this code born

Thank you veru much Josh Triplett!

Signed-off-by: Takeshi Banse <takebi@laafc.net>
Teach to select minibuffer window

If the `paste-buffer` is minibuffer, select the minibuffer-window.
This eliminates the modifications of the minibuffer-local-map.

Signed-off-by: Takeshi Banse <takebi@laafc.net>