Fix race condition during workspace changes
When changing workspaces, after focusing new window, wmaker handles all
pending events. If it receives another change-workspace combination,
you may end up with a workspace without any focused window.
Ctrf-F1 and Ctrl-F2 used to switch to 1st and 2nd workspaces.
Hold Ctrl and press F1 and F2 almost at the same time.
This patch ignores all change-workspace commands while workspace
change is in progress.
See also https://bugzilla.altlinux.org/show_bug.cgi?id=7230
[crmafra: Thanks to Alexey I. Froloff for the above explanation]