Allow carriers to choose any division as lead

[dohboy]

This would be an easy fix to the problem of providing CAP to the scout force. Currently they can only be assigned to support divisions in the same force. I know the "Provide CAP to" function is supposed to do this, but it never seems to work very well for me. I would still like to be able to assign individual squadrons to provide CAP for any division, but this is an easy fix that would muzzle me.