Just Pushed: Allow to control replication type (sync / async) for relevant operations

Just pushed support to allow to control the replication type for relevant
operations which include index, delete, and delete_by_query. It can be
controlled both as a global (node) level setting, and per operation. This
should benefit indexing performance for clients which can't push data fast
enough to elasticsearch. See more here:
http://github.com/elasticsearch/elasticsearch/issues/issue/196.

cheers,
shay.banon