userspace client
- rm -rf on fragmented directory
-- move the size check(s) on read from _read() into FileCache
- time out caps, wake up waiters on renewal
+ - link caps with mds session
- validate dn leases
- clean up ll_ interface, now that we have leases!
-- obey file_max
- clean up client mds session vs mdsmap behavior?
- client caps migration races
- caps need a seq number; reap logic needs to be a bit smarter