Merge pull request #1361 from unihorn/182

etcdserver: refactor cluster and clusterStore
main: add header
Merge pull request #1373 from jonboulle/header

main: add header
etcdserver: add member endpoint to peerurl
etcdserver: sort Members() in Cluster
Merge pull request #1375 from jonboulle/sort

etcdserver: sort Members() in Cluster
Merge pull request #1374 from xiangli-cmu/cluster_on_peerurl

etcdserver: add member endpoint to peerurl
main: fix proxy initialization and setupCluster
Merge pull request #1372 from jonboulle/proxy

main: fix proxy initialization and setupCluster
client: s/v2Prefix/DefaultV2KeysPrefix/
client: s/v2URL/v2KeysURL/
client: copy v2KeysPrefix to httpClient

It's poor form to muck with a global variable. Make a copy when the
httpClient object is instantiated to make httpClient.SetPrefix safe.