Log Message:
Update databases/elasticsearch to 5.1.2.

Aggregations::
- Allow terms aggregations on pure boolean scripts.
- IP range masks exclude the maximum address of the range.
- Fix `other_bucket` on the `filters` agg to be enabled if a key is set.

Allocation::
- Promote shadow replica to primary when initializing primary fails
- Trim in-sync allocations set only when it grows

Analysis::
- Pre-built analysis factories do not implement MultiTermAware
  correctly.

CRUD::
- Reject external versioning and explicit version numbers on create

Core::
- Support negative numbers in readVLong

Exceptions::
- Fixing shard recovery error message to report the number of docs
  correctly for each node

Index APIs::
- Ensure shrunk indices carry over version information from its source

Internal::
- Don't output null source node in RecoveryFailedException

Java REST Client::
- Don't use null charset in RequestLogger

Logging::
- Restores the original default format of search slow log

Mapping::
- Only update DocumentMapper if field type changes
- The `_all` default mapper is not completely configured.
- Fix MapperService.allEnabled().

Network::
- Disable the Netty recycler
- Tell Netty not to be unsafe in transport client

Nested Docs::
- Fix bug in query builder rewrite that ignores the ignore_unmapped
  option

Packaging::
- Another fix for handling of paths on Windows

Percolator::
- Fix NPE in percolator's 'now' range check for percolator queries with
  range queries

Plugins::
- Provide helpful error message if a plugin exists
- Add shutdown hook for closing CLI commands

Plugin Lang Painless::
- Update Painless Loop Counter to be Higher

Plugin Repository Azure::
- readonly on azure repository must be taken into account

Recovery::
- Fix primary relocation for shadow replicas
- Don't close store under CancellableThreads
- Use a fresh recovery id when retrying recoveries
- Allow flush/force_merge/upgrade on shard marked as relocated

Reindex API::
- Don't close rest client from its callback

Search::
- Improve concurrency of ShardCoreKeyMap.
- Make `-0` compare less than `+0` consistently.
- FiltersAggregationBuilder: rewriting filter queries, the same way as
  in FilterAggregationBuilder

Stats::
- Implement stats for geo_point and geo_shape field
- Use reader for doc stats
- Avoid NPE in NodeService#stats if HTTP is disabled
- Add support for "include_segment_file_sizes" in indices stats REST
  handler

Term Vectors::
- Fix _termvectors with preference to not hit NPE
- Return correct term statistics when a field is not found in a shard