changed locking to screen so that keys no longer count (only
mouse buttons and scroll lock toggled on). This is to deal
with the unreliability of key event reporting which can leave
us locked to a screen with no key physically pressed. The
result of this is that clients get key repeats and releases
without the corresponding key press. CKeyState handles this
by discarding repeat/release events on keys it hasn't seen go
down. Also made a few other minor fixes to win32 keyboard
handling.
This new design is simpler. For keyboard support, clients need only
implement 4 virtual methods on a class derived from CKeyState and
one trivial method in the class derived from CPlatformScreen, which
is now the superclass of platform screens instead of IPlatformScreen.
Keyboard methods have been removed from IPlatformScreen, IPrimaryScreen
and ISecondaryScreen. Also, all keyboard state tracking is now in
exactly one place (the CKeyState subclass) rather than in CScreen,
the platform screen, and the key mapper. Still need to convert Win32.
