Add disk stats to `/stats` output to make consistent

As pointed out by @fygrave in #285, `riak-admin status` shows
diak stats, but `/stats` does not. This fixes that.#285, `riak-admin status` shows
diak stats, but `/stats` does not. This fixes that.#285, `riak-admin status` shows
diak stats, but `/stats` does not. This fixes that.
Roll riak_kv version 1.4.0
Fix final multipart boundary when streaming 2i with max_results.
An error hunk in the 2i stream should terminate the multipart message.
Merge pull request #593 from basho/sdc-fix-2i-multipart

Fix final multipart boundary when streaming 2i with max_results.
Fix final multipart boundary when streaming 2i with max_results.
An error hunk in the 2i stream should terminate the multipart message.
Merge branch '1.4'
Merge pull request #383 from basho/rdb-eq-stats-status

Add disk stats to `/stats` output to make consistent
Merge remote-tracking branch 'basho/master' into jpg-feature-bitcask-deadbytes-stat