Fixed the EventHook() code so that it also works on Windows, sort of.

Fixed the EventHook() code so that it also works on Windows, sort of.
(The "sort of" is because it uses kbhit() to detect that the user
starts typing, and then no events are processed until they hit
return.)

Also fixed a nasty locking bug: EventHook() is called without the Tcl
lock set, so it can't use the ENTER_PYTHON and LEAVE_PYTHON macros,
which manipulate both the Python and the Tcl lock.  I now only acquire
and release the Python lock.

(Haven't tested this on Unix yet...)