Using a global array for action filters is bad. If two keyboard hit a modifier
at the same time, releaseing the first one will deactivate the filter and
thus the second keyboard can never release the modifier again.
(cherry picked from commit bfe6b4d2d9)
The former <X11/extensions/XKBsrv.h> has been pulled into the server now as
include/xkbsrv.h, and the world updated to look for it in the new place,
since it made no sense to define server API in an extension header. Any
further work along this line will need to do similar things with XKBgeom.h
and friends.