Adds test for cluster instance concurrent startup failure
Fixes problem with null comparisons and optional relationships
Merge pull request #579 from systay/optional-null-check

Fixes problem with null comparisons and optional relationships
Adds some debugging output in LearnerState and ElectionContext
Gives preference for electing as master the existing master if txIds match.

Moves DefaultElectionCredentialsProvider and friends to ha from cluster, since it is
 HA specific
Introduces HighAvailabilityMemberInfoProvider to decouple instance state info from HAGD
DefaultElectionCredentialsProvider now also provides info on current member status
ElectionState now asks the current master last for its election credentials, ensuring
 that its credentials are the most up to date
Whitespace and some cleanup in ElectionState
Updated the contributor list.
Removes looping over all instances in config when joining in ClusterJoin

This loop happens in parallel in ClusterState now.
Adds output of Paxos instance in StateTransitionLogger
Fixes issues with conversation handling, driven by cluster forming failures

Adds proper message header copying in places where it was missing, leading to
 mixup of conversations
Failed proposals will now keep the original conversation id header
Updates changelogs for 1.9.M05, expected tomorrow.
Merge pull request #580 from digitalstain/master-preference

Improvements around master election, giving preference to current master
typo