* 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
* 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
* added V8 context lifetime control options `--javascript.v8-contexts-max-invocations` and `--javascript.v8-contexts-max-age`
* make thread scheduling take into account most of the tasks dispatched via the io service
* fix buffer overruns in linenoise for long input lines
* don't make historian repeatedly print the same error messages that nothing can be done about
* make the implementations of the logging operator<<s not throw exceptions, so that logging does throw exceptions as an unintended side effect
* update CHANGELOG
* improve error message
* don't copy strings, but pass them by const reference
* reduce extractions to projections
* recycle string buffers in SocketTask
* micro optimizations for mmfiles indexes
* added special lookup function for _key
* moved function into the correct file
* speed up key buffer allocations a bit
* added noexcept specifier
* correctly name variable
* explicitly move bounds
* fix and speedup from/toPersistent functions
* reuse string from ManagedDocumentResult for multiple lookups
* use move-assign
* a bit less work for single server
* speedup AQL function HASH
* single fetch optimization
* performance optimization for the case when no documents need to be returned
* make reduce-extraction-to-projection a RocksDB-only optimizer rule
* cppcheck
* try to fix compile error on MacOS
* bug fix for MacOSX
* missing namespace (in Windows compile)
* 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.
* reduce extractions to projections
* recycle string buffers in SocketTask
* micro optimizations for mmfiles indexes
* added special lookup function for _key
* moved function into the correct file
* speed up key buffer allocations a bit
* added noexcept specifier
* correctly name variable
* explicitly move bounds
* fix and speedup from/toPersistent functions
* reuse string from ManagedDocumentResult for multiple lookups
* use move-assign
* a bit less work for single server
* speedup AQL function HASH
* single fetch optimization
* performance optimization for the case when no documents need to be returned
* make reduce-extraction-to-projection a RocksDB-only optimizer rule