Riak KV 3.0.18 - Internal NHS Release

This internal release helps with the operation of a Riak cluster with delete_mode set to keep:

• The nextgenrepl solution is enhanced with a configurable option to replicate reap requests from the riak_kv_reaper so that reap queries can be made whilst keeping clusters in full-sync.
• The $key query feature may now be configured to ignore tombstones when the backend is leveled to mimic the behaviour normally seen by queries when running other delete modes.