Exactly index sortkey with Lucene

Store sortkey as a long and implement the before and after operators
as numeric range queries.  This is a short-term hack until we have a
better idea of how to handle pagination without relying on a made up
string value stored on the change object.

Change-Id: Ibf7a8be281da8cd9e7ccc08bba600bbc2e0e962c
5 files changed