etcdserver: restore test coverage of cluster
Merge pull request #1238 from jonboulle/etcdserver_cluster

etcdserver: restore test coverage of cluster
raft: fix send
send should not attach current term to msgProp. Send should simply do proxy for msgProp without
changing its term. msgProp has a special term 0, which indicates that it is a local message.
Merge pull request #1240 from coreos/fix_proposal

raft: fix send
*:discovery hook up
Documentation: introduce the initial 0.5 clustering guide

Introduce the concepts of static initial cluster configuration and
document the flag migrations.
main: fail on peers/peers-file flags
Merge pull request #1244 from jonboulle/peers

main: fail on peers/peers-file flags
main/raft: write addNode ConfChange entries in log when start raft
main: use initial-cluster and initial-cluster-state flags

In preperation for adding the ability to join a machine to an existing
cluster force the user to specify whether they expect this to me a new
cluster or an active one.

The error for not specifying the initial-cluster-state is:
```
etcd: initial cluster state unset and no wal found
```
Merge pull request #1237 from philips/0.5-docs

use initial-cluster and initial-cluster-state flags
documentation: clustering guide fixes
etcdserver: move int64Slice into pkg/types/
Merge pull request #1247 from jonboulle/doc

documentation: clustering guide fixes
raft: refine initial entries logic in StartNode
main: fix temporary discovery cluster
Split config into a separate file and add sanity check and test
Merge pull request #1248 from jonboulle/disco

main: fix temporary discovery cluster
Merge pull request #1245 from unihorn/155

main/raft: write addNode ConfChange entries in log when start raft
tableize the test