raft: add handleHeartbeat
handleHeartbeat commits to the commit index in the message. It never decreases the
commit index of the raft state machine.
Merge pull request #1740 from xiang90/handleheartbeat

raft: add handleHeartbeat
raft: optimistically increase the next if the follower is already matched

This is useful since we want to pipeline the appendEntry requests. Without
enabling optimistic increasing, the second pipelining appendEntry request
will include the entries the first one has already sent out. We decrease
the next directly to match if the leader receives a rejection for a matched
follower. This happens if one pipelining request get lost and following ones
arrives at the follower.
create .godir
Merge pull request #1747 from proppy/master

create .godir
scripts: build-release add etcd-migrate

this tool is only temporary for the alphas but make sure it makes it in.
scripts: build-docker tag and use ENTRYPOINT

Use ENTRYPOINT so people can specify flags to etcd without providing the
binary.

Thanks to @hugod in IRC for pointing this out.
Merge pull request #1753 from philips/fixup-build-docker

scripts: build-docker tag and use ENTRYPOINT
Merge pull request #1752 from philips/include-etcd-migrate-in-releases

scripts: build-release add etcd-migrate
Merge pull request #1744 from xiang90/next

raft: optimistically increase the next if the follower is already matched
rafthttp: add streaming server and client
Merge pull request #1746 from yichengq/229

rafthttp: streaming server and client
etcdserver: autodetect v0.4 WALs and upgrade them to v0.5 automatically
fix import loop, add set to types, and fix comments
fix test import loop
add snapshotted integration test
Fix migration to allow snapshots to have the right IDs