Added basic support for 2i query. This involved some refactoring of the
test code to share functions between suites.
There is sill a need for a Part 2 as no tests currently cover removal of
index entries.
Some additional tests following previous refactoring for abstraction,
primarily to make manifest print safer an dprove co-existence of Riak
and non-Riak objects.
The object tag "o" which was taken from eleveldb has been an extended to
allow for specific functions to be triggered for different object types,
in particular when extracting metadata for stroing in the Ledger.
There is now a riak tag (o_rkv@v1), and in theory other tags can be
added and used, as long as their is an appropriate set of functions in
the leveled_codec.
