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.
on every key press and release so we don't have to updateKeys()
in isLockedToScreen(). However, if any key appears to be down
we still call updateKeys() to double check that it's really down.
If not we note the spurious lock and don't lock to the screen.
crs