kes Separate NumVolumes in SD to NumReadVolumes and NumWrite volumes so
that migration writing to multiple volumes doesn't mess up reading
Volumes. This should fix bug #720 -- multivol migration fails.
kes Make migration SQL look only for Type='B' jobs to migrate. This should
fix bug #724 jobs getting migrated twice.
kes Convert remaining dev_cap(dev, ...) to use dev->has_cap().
kes Implement dev->clear_cap() and dev->set_cap() methods.
kes Turn off disk seeking on restore for DVDs since I am not 100%
sure it works.