Added TODO for adding a setting for silently ignoring Riak backends that don't support indexes
Added some http header constants
Turned RiakIntIndex into RiakLongIndex because Riak stores values as 64-bit (unsigned) numbers
Cleaned up the HtpRiakclient imports a bit
Fixed a bug where RiakValue.toMeta didn't pass along its indexes
Removed old commented apply methods from RiakValue
Implemented HttpRiakClient support for secondary indexes, mapping to and from the relevant HTTP headers
Added some basic util traits for writing tests
WIP: First 4 unit tests for storing and retrieving with indexes