Update to elasticsearch 1.2.0

Hi,

A small initial patch to upgrade fsriver to elasticsearch 1.2.0. Some classes have disappeared in recent elasticsearch distribution, such as RestXContentBuilder. We have followed the same approach than in the mongodb plugin, i.e., copy pasting the original classes into the distrib.
With respect to the unit tests, on our side some of them are failing randomly. We have tried to debug it, but without success. It looks like some problem with file timestamp or due to the random order of the execution of the tests.