Make sure the command `move <direction>` properly sends the workspace
focus ipc event required for i3bar to be properly updated and redrawn.
Make `ipc_send_workspace_focus_event publicly available from ipc.h for
more flexible event sending.
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.
