Try:
./etcdctl put foo bar
./etcdctl del foo
./etcdctl compact 3
restart etcd
./etcdctl get foo
mvcc: required revision has been compacted
The error is unexpected when range over the head revision.
Internally, we incorrectly set current revision smaller than the
compacted revision when we remove all keys around compacted revision.
This commit fixes the issue by recovering the current revision at least
to compacted revision.
