* make TTL indexes behave like other indexes on creation
if a TTL index is already present on a collection, the previous behavior
was to make subsequent calls to `ensureIndex` fail unconditionally with
the error "there can only be one ttl index per collection".
now, we are comparing the attributes of the to-be-created index with the
attributes of the existing TTL index and make it only fail when the
attributes differ. if the attributes are identical, the `ensureIndex`
call succeeds and returns the existing index.
* added tests
* updated CHANGELOG
* issue 381.4.1: create a separate IResearchLink implementation for use with ClusterEngine
* backport: ensure StorageEngineMock assigns unique transaction ids
* delegate index normalization on the ClusterEngine to the 'actualEngine'
* remove some non-unused V8 persistents
* do not throw that many bogus assertions
* do not rely on server role being defined
* slightly better debug output for V8 context debugging
* fix collection ids in inventory response
* simplify bootstrap a bit
* slightly better error handling
* make elapsed time a queryable value
* use less memory for stub collections
* added assertions that will always make sense
* added assertions
* do not garbage-collect while waiting
* less copying of parameters
* do not show "load indexes into memory" buttons for mmfiles engine
as all indexes are in memory anyway
* when a collection is truncated via the web interface, flush the WAL and rotate all active journals
this will make close all open journals on leader and followers and make them subject to compaction opportunities
* fix invalid server id values being passed from web interface to backend
* introduce afterTruncate method for indexes
* added test case for issue #3447
* updated CHANGELOG
* don't warn about replicationFactor for system collections
* check that the queries actually use the geo index and not some other index
* properly report error in web interface
* fix some internals checks that made truncate fail for bigger collections in maintainer mode
* also run a compact() operation after a serious truncate
in order to make iteration over the truncated range much faster
when the collection is next accessed
* increase default maximum number of V8 contexts to at least 16
Jan
Wilfried Goesgens
Jan Christoph Uhde
Dan Larkin-York
Vasiliy
Frank Celler
Simon