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.
using low-level keyboard hooks, fixed handling of the global
keyboard layout dead key buffer, fixed identification of dead
keys, fixed synthesis of AltGr (now using right-alt instead
of left-alt), now using VK_DECIMAL for Separator key, fixed
bug where an unmappable key was treated as virtual key 0xff,
and added support for shift-space (shift was being discarded).
Also fixed failure to hide cursor when leaving primary screen
and added support for handling PrintScreen key.
crs