Core: add debug logging to InternalEngine.close
Update multi-get.asciidoc

Documented that the fields parameter can be passed in the query string.

Closes #4006
Docs: Improve the exists/missing filters documentation

Closes #7274
Update datehistogram-aggregation.asciidoc

Clarified use of fractional time units in the date histo agg.

Closes #7957
typo fixes - https://github.com/vlajos/misspell_fixer

Closes #8323
fix mention of Apache License, version 2.

Closes #8400
Merge https://github.com/elasticsearch/elasticsearch into es-merge-nov08