* Add copyright notices to all files which don't have one.

* docs/license.txt: Renamed to...
* docs/LICENSE.TXT: This.
* docs/FTL.txt: Renamed to...
* docs/FTL.TXT: This.
* docs/GPL.txt: Renamed to...
* docs/GPL.TXT: This.

* docs/PATENTS: Slightly reworded.  Suggested by Sylvain Beucler
<beuc@gnu.org>.