+con #3551 Buffer messages in cluster client

* Stash when establishing connection to receptionist
=clu #3600 Disable Cluster assertInvariants checks by default

* asserts can be enabled by system property 'akka.cluster.assert=on'
!rem, clu, mul #3154 Upgrade protobuf to 2.5.0 and add an SBT task

* Added an SBT task to compile protobuf files with protoc
* Upgraded protobuf to 2.5.0 which is the current stable
Merge pull request #1724 from akka/wip-3154-upgrade-to-protobuf-2.5.0-ban

!rem, clu, mul #3154 Upgrade protobuf to 2.5.0 and add an SBT task
Merge pull request #1714 from akka/wip-3551-buffer-cluster-client-patriknw

+con #3551 Buffer messages in cluster client
+con #3595 Use remote death watch in cluster client
Merge pull request #1716 from akka/wip-3595-cluster-client-remote-death-watch-patriknw

+con #3595 Use remote death watch in cluster client
Merge pull request #1723 from akka/wip-3600-disable-assertInvariants-patriknw

=clu #3600 Disable Cluster assertInvariants checks by default
Merge remote-tracking branch: upstream/master