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: streaming server and client
change
add streamer.go
address more changes
adress more comments
split sender
hehe
haha