Display "locking…" message when grabbing the pointer/keyboard,
after at least 250 ms of unfruitful attempts. If grabbing
eventually fails, application will not fork and return 1.
See also:
http://article.gmane.org/gmane.linux.kernel/1268792
The C compiler will handle (void) as "no arguments" and () as "variadic
function" (equivalent to (...)) which might lead to subtle errors, such
as the one which was fixed with commit 0ea64ae4.
