Licence: Relicence all Pachi from MIT to GPLv2

By now, Pachi is too large and powerful for my taste to be kept as public domain.

uct/COPYING → COPYING

@@ -1,8 +1,3 @@
-Note that the code in this engine can be redistributed under GPLv2,
-or at your option, any later version.
-
------------------------------------------------------------------------
-
 		    GNU GENERAL PUBLIC LICENSE
 		       Version 2, June 1991
 

README

@@ -52,10 +52,18 @@ be at the same time kept as simple as possible).
 Licence
 -------
 
-Pachi is under the MIT licence (almost public domain) so that as
-many people as possible can use it; if you use it to create your engine,
-appropriate credits would be appreciated. Some of the bundled engines
-or policies are under a more restrictive licence (GPL).
+Pachi is distributed under the GPLv2 licence (see the COPYING file for
+details and full text of the licence); you are welcome to tweak it as
+you wish (contributing back upstream is welcome) and distribute
+it freely, but only together with the source code. You are welcome
+to make private modifications to the code (e.g. try new algorithms and
+approaches), use them internally or even to have your bot play on the
+internet and enter competitions, but as soon as you want to release it
+to the public, you need to release the source code as well.
+
+One exception is the Autotest framework, which is licenced under the
+terms of the MIT licence (close to public domain) - you are free to
+use it any way you wish.
 
 
 To build Pachi, simply type: