kes Rework the reservation system to take into account that the Director

     might give us a Volume that is different from the current one being
     used, and to ensure that we don't exceed Maximum Volume Jobs.
     This fixes (mostly) bug #947 '  Maximum Volume Jobs = 1 produces
     fatal error with multiple jobs running'
kes  Add more debug code in reservation system.
kes  Implement maxvol-test to check bug #947.