* Add security check in AgencyComm::sendWithFailover.
* some cleanup
* added some more tests
* add typeName() to AgencyCommTransaction to make the transaction type printable in debug messages
* improve debuggability
* Return connection timeout condition as being same as aborted operation. Otherwise ClusterCommResult::fromError() will mark sendWasComplete as true.
* make test of connect_time specific to the TIMEOUT error
* do not use V8 variant of AQL functions in early optimization stage when a C++ variant is available
* additionally, simplify AQL function definitions and aliases
* warn when more than 90% of max mappings are in use
* added C++ variant of replication catchup
* added `--log.role` option
* updated CHANGELOG
* removed non-existing scheduler.threads option from config
* removed useless __FILE__, __LINE__ invocations
* updated CHANGELOG
* allow a priority V8 context
* remove TRI_CORE_MEM_ZONE
* try to fix Windows errors & warnings
* cleanup
* removed memory zones altogether
* exclude system collections from collection tests
* Take out 503 timeouts altogether.
* Overhaul of AgencyComm::sendWithFailover loop.
* Let performRequests optionally ignore 404 coll not found.
* Fix error message "database not found" when AgencyComm failed.
* Add log entries in Agency if locks are acquired too slowly.
* Reexecute the javascript cluster sync stuff even if there was no plan/current change...So failed sync jobs can retry later...
* Cover callbacks in Communicator by lock. This fixes https://github.com/arangodb/planning/issues/370
* Put in delay in waiting for leader in agency test.
* Schmutz logging to heartbeat topic.
* Add more lock time diagnostic in agent.
* Switch on agencycomm tracing in coordinator.