This patch makes the numlock+capslock tracking logic only look at
keydown events. Without this patch the vnc server will insert
bogous capslock keypress in case it sees the following key sequence:
shift down --- 'A' down --- shift up --- 'A' up
^ here
It doesn't hurt with a PS/2 keyboard, but it disturbs the USB Keyboard.
And with the key event queue just added to the usb keyboard the guest
will actually notice.