* move IResearchViewSort into separate unit
* ensure sort is propagated to IResearchLink
* update iresearch and extend some tests
* implement insertion of sorted values, store value comparator in link
* add tests for VPackComparer
* minor cleanup
* fix issue with sort definiton propagation
* propagate error message from index factory
* add integration tests for sorted indexes, single server
* initial implementation of IResearchViewMergeExecutor
* move iresearch::VPackComparer to separate translation unit
* store collection in IndexReadBuffer for IResearchViewMergeExecutor
* set primary sort from optimizer rule
* add some tests for sorted view case
* extend IResearchViewNode tests
* simplify primary sort definition
* pretty print order condition covered by arangosearch in query explanation
* fix compilation with g++-8
* address catch test failures
* fix tests
* adjust arangosearch optimizer rule to optimize sort in case of cluster
* make tests for sorted indexes work in cluster too
* fix tests
* extend js tests for sorted indices
* fix keyword in query explainer
* ensure sort-limit rule works with views
* backport ngram analyzer fix from upstream
* address jslint errors
* modify IResearchViewSort to support boolean direction specification format
* add some tests
* add tests
* add skip functionality
* extend tests
* add more catch tests
* inline some methods
* address jslint errors
* extend catch tests to reproduce the failure
* add some tests for check fullcount
* add more tests
* extend tests
* temporarily comment out broken tests
* extend js tests
* address review comments
* address jslint errors
* update iresearch
* issue 511.4: ensure IResearchLink can be initialized without view as required for db-server, minor code fixes and cleanup
* remove unnessesary checks
* revert last change due to test failures
* fix typo in change revert
* try to address random test failures
* issue 496.5: minor API cleanup and error reportin enhancements, update iresearch to commit d69f7bd184e009da7bf0a478efd34a0c85b74291
* add workaround for shell-collection-rocksdb-noncluster.js::testSystemSpecial test failure
* fix typo
* issue 496.3: move more coordinator-related logic out of TRI_vocbase_t, rename some arangosearch view configuration parameters, remove some consolidation policies, update iresearch to revision 6fd9760d81b136f769e277ea5b8f53996ed7a1ca
* address potential deadlock between link creation and FlushThread
* remove code causing nullptr access
* add back lock around reader reopen
* revert: address potential deadlock between link creation and FlushThread
* invalidate payload for each field in FieldIterator before setting a value
* issue 496.1: switch scope of responsibility between a TRI_vocbase_t and a LogicalView in respect to view creation/deletion
* backport: address test failures
* backport: ensure arangosearch links get exported in the dump
* backport: ensure view is created during restore on the coordinator
* Updates for ArangoSearch DDL tests, IResearchView unregistration and known issues
* Add fix for internal issue 483
* issue 485: ensure LogicalDataSource::drop() is called on vocbase drop
* add missed change
* backport: address race between make(...) and async job
* add another missed change
* backport: ensure recursive lock reports itself as locked correctly
* backport: address test failure on mmfiles
* backport: remove redundant lock already held by async task
* backport: reset reader before unlinking directory