[RECOVERY] Increment Store refcount on RecoveryTarget

We should make sure we have incremented the store refcount
before we start the recovery on the recovyer target.

Closes #6844
[ENGINE] Mark store as corrupted before sending failed shard

We have to mark a shard as corrupted if necessary before the
shard failed event is fired ie. before we call the corresponding
listener in the engine. Otherwise the shard might be re-allocated
on the same node and just started up without being marked as corrupted.

Relates to #5924
[Transport] possible NPE during shutdown for requests using timeouts

Closes #6849
significant terms: infrastructure for changing easily the significance heuristic

This commit adds the infrastructure to allow pluging in different
measures for computing the significance of a term.
Significance measures can be provided externally by overriding

- SignificanceHeuristic
- SignificanceHeuristicBuilder
- SignificanceHeuristicParser

closes #6561
Analysis: Improve Hunspell error messages

The Hunspell service would throw a confusing error message if more than
one affix file was present.  This commit distinguishes between the two
error cases: where there are no affix files and when there are too many
affix files.

Also implements lazy dictionary loading, which was used in the tests
but not implemented.

Closes #6850
[TEST] For connection rules make TransportAddress the identity instead of DiscoveryNode.

For unicast ping the DiscoveryNode identity is based on its id, which in that stage is a dummy value, this breaks any rule in the mock tran
However the TransportAddress is a valid value in unicast ping and all other places, so that is a better alternative.

Closes #6836