Notice - Gateway changes in next version


I thought long and hard about this one, and decided to do it in order to
better support future elasticsearch version. I have changed the format of
the gateway storage to allow to support for easily changing it without
breaking backward compatibility. I consider gateway changes as something
that needs to be frowned upon, and I apologize in advance for this change.
This means that upgrading to the next version will require a reindexing of
the data, booting from a clean gateway storage.

For this reason, the next version will be 0.8 (which includes several
improvements, the most important one is a workaround for a Lucene bug in
memory management). I am trying to see if I can beef it up a bit more with
features, so it will deserve the 0.8 release (aside from the HDFS gateway),
but it won't linger for long (hopefully, at max, a week).

The changes are already in master.