kbfsblock: protocol helper for getting ref counts
kbfsblock: protocol helper for getting ref counts

Issue: KBFS-3661

keybase/client,keybase/client,keybase/client,keybase/kbfs,keybase/kbfs,keybase/kbfs,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/kbfs