Add Polish alphabet.  Fix AltGr keyboard events.

This fixes a reported problem under Windows (it was probably an issue
on other platforms, too) where, if you're using a keyboard that requires
AltGr in order to type Scrabble letters on the board, they simply won't
type.   For example, the Windows "Polish Programmers" keyboard.

Polish alphabet submitted by Adam Klimont, and tested by me.  Dictionary
to come soon.