* allow to access last operation tick of the transaction
* modify IResearchLink to rely on last commtted tick
* get rid of writing arangosearch markers to WAL
* further implementation
* local changes in iresearch
* add recovery states
* properly handle link creation during recovery
* adjust test cases
* properly handle nested transactions
* ungreylist recovery tests
* add more recovery tests
* do not use transaction to pass recovery tick
* do not store recoveryTick in MMFilesRecoveryState
* adjust tests
* fix mmfiles
* cleanup
* add context validity check
* fix tests
* fix more tests
* ensure subscription is not being released during commit
* address review comment
* final cleanup
* fix crash
* fix tests
* address test failures
* address review comments
* address review comments
* properly set recovery tick even if no recovery happened
# Conflicts:
# arangod/IResearch/IResearchLink.cpp
* issue 511.9.1: track DataSource instance instead of only its name in QueryCache
* address use of invalid function
* fix expected test result
* address merge issue
* Switching from ttl to supervision based failover mechanism
* Allowing canceling of ongoing actions
* refactored asyncjobmanager
* refactoring some code
* adding read-only flag
* catching some exceptions to reduce log pollution, removing unnecessary code, removing tests for _changeMode
* fixing "createsANewDatabaseWithAnInvalidUser"
* auth = off does not longer make everyone superuser
* Fixing cluster_sync and maybe resilience
* Make isRestore work in the cluster.
This covers sharded collections with default sharding and non-default
sharding.
* always use locally generate revision ids for storing and looking up documents