Add keyc->postdown, which represents the key state as of the last mieqEnqueue
call, and use it when we need to know the posted state, instead of the
processed state (keyc->down). Add small functions to getevents.c to query and
modify key state in postdown and use them all through, eliminating previously
broken uses.
(cherry picked from commit 81c28ffd2b)
f73fd98a86