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.
of that file in existance, not all of which have all the symbols we
require and none of which provide any convenient means of telling
what groups of symbols they define.
crs