Added scoring support to `has_child` and `has_parent` queries.

Added score support to `has_child` and `has_parent` queries. Both queries support a score_type option. The has_child support the same options as the top_children query and the none option which is the default and yields the current behaviour. The has_parent query support the score type options: score and none. The latter is the default and yields the current behaviour.

If the score_type is set to a value other than none then the has_parent query map the matched parent score into the related children documents. The has_child query then map the matched children documents into the related parent document. The score_type on both queries defines how the children documents scores are mapped in the parent documents. Both queries are executed in two phases. First phase collects the parent uid values of matching documents with an aggregated score per parent uid value. In the second phase either child or parent typed documents are emitted as hit that have the same parent uid value as found during the first phase. The score computed in the first phase will be used as score.

Closes #2502
Improved explain support for nested query.

Closes #2503
Minor changes to the parent / child benchmark.
Plugins Installer: Allow to download plugins from download.elasticsearch.org
closes #2507.
Pass topScorer=false to sub-scorers if a scorer is wrapped. Wrapped BooleanQuery can return collect-only scorers. See #2505
cleanup
Allow highlighting on wildcard fields.. ie, comment_*
closes #2396
ShardSearchFailure handling of exception does not take actual into account for status
fixes #2495
match_all filter with empty array (instead of obj) fires exception when used with facets
fixes #2493
optimize filtered query with match_all filter
simply just use the query in that case, and don't add the filter overhead
fix failed tests due to wrapping failures with mapping parsing exception
fix copy/paste bug where null stopWords is passed causing an NPE
allow index and type to be specified as arrays in MultiSearchRequest
cleanup
fix type to types
Update settings: Allow to dynamically update thread pool settings

Closes #2509
upgrade to netty 3.6.0
upgrade to jackson 2.1.1
add a sleep to make sure settings are applied
add 0.20.3