5882: put back Elasticsearch's 1.1 defaults for ConcurrentMergeScheduler
#6120 Remove SerialMergeScheduler (master only)

It's dangerous to expose SerialMergeScheduler as an option: since it only allows one merge at a time, it can easily cause merging to fall behind.

Closes #6120
#5882: fix docs
#6081: set IO throttling back to 20 MB/sec now that #6018 is fixed
Change key to keyed
fixed MetaData#concreteIndices to throw exception with a single index argument in case allowNoIndices == false and ignoreUnavailable == true

Closes #6137
improved IndicesOptions javadocs
Fix for benchmark test timeout

Lower number of random requests generated for each test so as not to
timeout on heavy tests.

Addresses #6094
Fix for hanging aborted snapshot during node shutdown

If a node is shutdown while a snapshot that runs on this node is aborted, it might cause the snapshot process to hang.

Closes #5958
[DOCS] Added "Aggregation" to all aggs titles
Log script change/add and removal at INFO level

Closes #6104
Significant_terms agg: added option for a background_filter to define background context for analysis of term frequencies

Closes #5944
refactor: unify terms and significant_terms parsing

Both need the requiredSize, shardSize, minDocCount and shardMinDocCount.
Parsing should not be duplicated.
refactor: make requiredSize, shardSize, minDocCount and shardMinDocCount a single parameter

every class using these parameters has their own member where these four
are stored. This clutters the code. Because they mostly needed together
it might make sense to group them.
I hope that this makes the code more readable and also that if avoids
errors such as mixing up the int/long parameters in the future.
add failing test for shard_min_doc_count
use shard_min_doc_count also in TermsAggregation

This was discussed in issue #6041 and #5998 .
add documentation of `shard_min_doc_count`