Remove intern calls on FieldMapper#Names
remove internal callas on FieldMappers#Names, we properly reuse FieldMapper, so there is no need to try and call intern in order to reuse the names. This can be heavy with many fields and continuous mapping parsing.
closes #6747
[API SPEC] Update indicies.stats group param
add more options to many mappings test
[ENGINE] Prevent NPE if engine is closed while version map is checked

We check if the version map needs to be refreshed after we released
the readlock which can cause the the engine being closed before we
read the value from the volatile `indexWriter` field which can cause an
NPE on the indexing thread. This commit also fixes a potential uncaught
exception if the refresh failed due to the engine being already closed.

Relates to #6443
Closes #6786
Remove Lucene's deprecated PatternTokenizer

Instead of using the PatternTokenizer, the functionality was replicated by using Lucene's StopFilter, PatterTokenizer and LowerCaseFilter

Closes #6717
[Engine] checkVersionMapRefresh shouldn't use indexWriter.getConfig(). We run it out of lock, the indexWriter may be closed..

Relates to #6443, #6786

Closes #6794
Update preference.asciidoc

Clarify that `preference` is a query string parameter only
and provide an example.
[Code] Control whether MapperService docMapper iterator should contain DEFAULT_MAPPING

At the moment one can iterate the MapperService to go through all document mappers. This includes the document mapper of DEFAULT_MAPPING, which may be surprising and lead to unintended results. This commit removes the Iterable implementation and add a docMappers method that asks the caller to make an explicit choice

Closes #6793
Store: Before removing shard physically from disk verify that another node in the cluster actually holds an active shard copy.

Closes #6692
Improve Settings#get lookup for camel case support
Today, if we miss on a get on setting, we try its camel case version. The assumption is that in our code, we never use camel case to lookup a setting, but we want to support camel case if the user provided one.
This can be expensive (#toCamelCase) when the get on the setting is done in a tight call, which is evident when running the allocation deciders as part of the reroute logic.
Instead of doing the camel case check on get, prepare an additional map that includes all the settings that are provided as came case, and try and lookup from it if needed.
closes #6765
Add v1.2.3 to Version.java
Fix typo in Hunspell logging
Docs: Update plugins.asciidoc

Closes #6683
Docs: New entry/front-end

Adding, Calaca, a simple search client for Elasticsearch.

Closes #6754
[Test] BackgroundIndexer uses the wrong logger

Closes #6781
Merge pull request #6792 from areek/fix/6717

Remove Lucene's deprecated PatternAnalyzer
Upgrade to jackson core 2.4.1.1
Note, we had to disable the symbol overflow, since the many mapping case was tripping it
closes #6789
Modify command window title (windows)

When launching multiple nodes in MS Windows env, batch command window does not come by default with any title.

This patch add `Elasticsearch VERSION` as a title, where VERSION is the current elasticsearch version.

Same for `plugin.bat` and `service.bat`.

Closes #6336
Closes #6752
[TEST] move more tests to assertBusy from awaitBusy
Disable JSONP by default
By default, disable the option to use JSONP in our REST layer
closes #6795