* 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
* start maintenance arangosearch threads after recovery is done
* ensure flush subscription is not being deallocated while in use
* add some tests
* properly determine storage engine
* adjust default view options
* stick to old index meta format in 3.5
* address test failures
* and cluster tests
* ensure flush subscriptions are being unsubscribed
* update tick even if no changes happened
* remove debug output
* fix test
* address review comments
* address test failures
* issue 466.4: implement persistence of IResearchLink WAL flush marker
* address enterprise test failure
* address test failures
* treat missing collections/indexes as potentially removed
* change view asertios to match collection assertions
* convert assertions to exceptions since they are possible
* revert assertion removal since assertions are actually valid for coordinator
* address scenario where link is dropped twice
* check for data store state before returning error
* revert last change since it's not valid for MMFiles
Andrey Abramov
Dan Larkin-York
Jan
Vasiliy
Simon
Frank Celler