[Logging] added trace logging to TransportShardSingleOperationAction

And enabled them on SimpleRecoveryTests.testSimpleRecovery
[TEST] wait for no pending tasks so processed all mappings
[TEST] also assert that put mapping is ack'ed
[QUERY] Remove Queries#optimizeQuery(...)

This method tires to optimize boolean queries if there is only
one clause. Yet BooleanQuery already does that internally This
optimization is unneeded.

Closes #6743
[TEST] Close threadpool once test searchcontext is released
Improve performance for many new fields introduction in mapping
When we have many new fields keep being introduced, the immutable open map we used becomes more and more expensive because of its clone characteristics, and we use it in several places.

The usage semantics of it allows us to also use a CHM if we want to, but it would be nice to still maintain the concurrency aspects of volatile immutable map when the number of fields is sane.

Introduce a new map like data structure, that can switch internally to CHM when a certain threshold is met.

Also add a benchmark class to exploit the many new field mappings use case, which shows significant gains by using this change, to a level where mapping introduction is no longer a significant bottleneck.
closes #6707
Improve pending api to include current executing class
the pending tasks api will now include the current executing tasks (with a proper marker boolean flag)
this will also help in tests that wait for no pending tasks, to also wait till the current executing task is done
closes #6744
Add license header to ManyMappingsBenchmark.java
[TEST] only mark the event as processed when its out of its execution
[TEST] test didn't take into account other cluster service tasks
The pending tests on an actual node should take into account that other tasks might be executing on that node, thus failing when it happens
[TEST] remove repeat lefover...
[TEST] wait for threads to finish writing before checking
we need to make sure we wait for all threads to finish executing, since there might still be a thread around even post await (i.e. just starting) performing updates
Call callback on actual mapping processed
only callback the registered callback listeners when mapping have actually been processed...
closes #6748
Upgrade Jackson to 2.4.1
closes #6757
Docs: Language analyzers
Clarified the use of stem_exclusion and the keyword_marker
token filter

Closes #6613
Docs: fixed a typo in the docs

Closes: #6718
Docs: Update histogram-aggregation.asciidoc

filter in a filtered query should be under "filter" key

Closes #6738
Allow primaries that have never been allocated to be allocated if under the low watermark

Fixes #6196
[Relocation] process pending mapping update in phase 2

During phase1 we copy over all lucene segments. These may refer to mapping updates that are still queued up to be sent to master. We must make sure those pending updates are processed before completing the relocation.

Relates to #6648

Closes #6762
Query DSL: Improved explanation for match_phrase_prefix

The match_phrase_prefix provided the same explanation as the match_phrase
query. There was no indication that the last term was run as a prefix
query.

This change marks the last term (or terms if there are multiple terms
in the same position) with a *

Closes #2449