Update riak to 1.2.1.

Bugfixes:
 * LevelDB - Restrict number of input files to a compaction.
 * riak_pipe - Avoid race to code:load_file by using code:ensure_loaded instead
 * riak - Beams in basho-patches don't take precedence over existing code
 * merge_index - Fix iterator API (Thanks to Arnaud Wetzel)
 * riak_core - Restart vnode worker pool in case of crash
 * riak_kv - Resolve 2I timeout error from case clause
 * riak_kv - Add retry on eleveldb lock errors during open for up to 1 minute.
 * bitcask - Adds "grace period" to stop just-written files from expiring
 * erlang_js - ejsLog() kills the erlang vm in a reduce
 * bitcask - Validate hint files generated after merge
 * riak_core - Remove publish_capabilities race condition