CORS: Support regular expressions for origin to match against

This commit adds regular expression support for the allow-origin
header depending on the value of the request `Origin` header.

The existing HttpRequestBuilder is also extended to support the
OPTIONS HTTP method.

Relates #5601
Closes #6891
Docs: Added new entry for the SIREn plugin.

Closes #6961
Docs: Changing ES_MAX_MEM default from '1gb' to '1g'

If you set ES_HEAP_SIZE to '1gb' as suggested, Java will yield an "Invalid initial heap size".

Closes #6824
Aggregations: Added an option to show the upper bound of the error for the terms aggregation.

This is only applicable when the order is set to _count.  The upper bound of the error in the doc count is calculated by summing the doc count of the last term on each shard which did not return the term.  The implementation calculates the error by summing the doc count for the last term on each shard for which the term IS returned and then subtracts this value from the sum of the doc counts for the last term from ALL shards.

Closes #6696
Add multi_field support for Mapper externalValue (plugins)

In context of mapper attachment and other mapper plugins, when dealing with multi fields, sub fields never get the `externalValue` although it was set.

Here is a full script which reproduce the issue when used with mapper attachment plugin:

```
DELETE /test

PUT /test
{
    "mappings": {
        "test": {
            "properties": {
                "f": {
                    "type": "attachment",
                    "fields": {
                        "f": {
                            "analyzer": "english",
                            "fields": {
                                "no_stemming": {
                                    "type": "string",
                                    "store": "yes",
                                    "analyzer": "standard"
                                }
                            }
                        }
                    }
                }
            }
        }
    }
}

PUT /test/test/1
{
    "f": "VGhlIHF1aWNrIGJyb3duIGZveGVz"
}

GET /test/_search
{
    "query": {
        "match": {
           "f": "quick"
        }
    }
}

GET /test/_search
{
    "query": {
        "match": {
           "f.no_stemming": "quick"
        }
    }
}

GET /test/test/1?fields=f.no_stemming
```

Related to https://github.com/elasticsearch/elasticsearch-mapper-attachments/issues/57

Closes #5402.
Mappings: Enforce non-null settings.

No that we are using the index created version to make index-time decisions,
assuming that the version is the current version when settings are null is
very error-prone. Instead we should ensure that settings are always non-null
and contain the version when the index was created.

Close #7032
Test: more verbosity for this test on failure
Docs: Reorganised the search-shards API docs
Docs: Removed search-shards from request-body
Docs: Fixed path to search-shards
Update nested-query.asciidoc

Changed score_mode `total` to `sum` to be consistent with parent-child etc
Docs: fix documentation for bloom filter defaults
The `nested` aggregator should also resolve and use the parentFilter of the closest `reverse_nested` aggregator.

Closes #6994
Closes #7048
Aggregations: fixed value count so it can be used in terms order

Closes #7050
[TEST] Ignore Lucene40 codec
Docs: Add Drupal Search API Elasticsearch module

The module at drupal.org/project/elasticsearch has been abandoned. The Search API Elasticsearch module allows Drupal to use Elasticsearch as a backend for Search API.

Closes #7001
[TEST] All shards should be allocated before snapshotting.
Update request-body.asciidoc

Added link from `timeout` to time-units

Closes #6361
Add HierarchyCircuitBreakerService

Adds a breaker for request BigArrays, which are used for parent/child
queries as well as some aggregations. Certain operations like Netty HTTP
responses and transport responses increment the breaker, but will not
trip.

This also changes the output of the nodes' stats endpoint to show the
parent breaker as well as the fielddata and request breakers.

There are a number of new settings for breakers now:

`indices.breaker.total.limit`: starting limit for all memory-use breaker,
defaults to 70%

`indices.breaker.fielddata.limit`: starting limit for fielddata breaker,
defaults to 60%
`indices.breaker.fielddata.overhead`: overhead for fielddata breaker
estimations, defaults to 1.03

(the fielddata breaker settings also use the backwards-compatible
setting `indices.fielddata.breaker.limit` and
`indices.fielddata.breaker.overhead`)

`indices.breaker.request.limit`: starting limit for request breaker,
defaults to 40%
`indices.breaker.request.overhead`: request breaker estimation overhead,
defaults to 1.0

The breaker service infrastructure is now generic and opens the path to
adding additional circuit breakers in the future.

Fixes #6129

Conflicts:
	src/main/java/org/elasticsearch/index/fielddata/IndexFieldData.java
	src/main/java/org/elasticsearch/index/fielddata/IndexFieldDataService.java
	src/main/java/org/elasticsearch/index/fielddata/RamAccountingTermsEnum.java
	src/main/java/org/elasticsearch/index/fielddata/ordinals/GlobalOrdinalsBuilder.java
	src/main/java/org/elasticsearch/index/fielddata/ordinals/InternalGlobalOrdinalsBuilder.java
	src/main/java/org/elasticsearch/index/fielddata/plain/AbstractIndexOrdinalsFieldData.java
	src/main/java/org/elasticsearch/index/fielddata/plain/DisabledIndexFieldData.java
	src/main/java/org/elasticsearch/index/fielddata/plain/IndexIndexFieldData.java
	src/main/java/org/elasticsearch/index/fielddata/plain/NonEstimatingEstimator.java
	src/main/java/org/elasticsearch/index/fielddata/plain/PackedArrayIndexFieldData.java
	src/main/java/org/elasticsearch/index/fielddata/plain/ParentChildIndexFieldData.java
	src/main/java/org/elasticsearch/index/fielddata/plain/SortedSetDVOrdinalsIndexFieldData.java
	src/main/java/org/elasticsearch/node/internal/InternalNode.java
	src/test/java/org/elasticsearch/index/aliases/IndexAliasesServiceTests.java
	src/test/java/org/elasticsearch/index/codec/CodecTests.java
	src/test/java/org/elasticsearch/index/fielddata/AbstractFieldDataTests.java
	src/test/java/org/elasticsearch/index/fielddata/IndexFieldDataServiceTests.java
	src/test/java/org/elasticsearch/index/mapper/MapperTestUtils.java
	src/test/java/org/elasticsearch/index/query/IndexQueryParserFilterCachingTests.java
	src/test/java/org/elasticsearch/index/query/SimpleIndexQueryParserTests.java
	src/test/java/org/elasticsearch/index/query/guice/IndexQueryParserModuleTests.java
	src/test/java/org/elasticsearch/index/search/FieldDataTermsFilterTests.java
	src/test/java/org/elasticsearch/index/search/child/ChildrenConstantScoreQueryTests.java
	src/test/java/org/elasticsearch/index/similarity/SimilarityTests.java
Change logging level for circuit breaking to warn