Ability to change bitcask key expiry without a node restart [JIRA: RIAK-2413]

[michellep-basho]

customer "must have" request received 24 July 13

[slfritchie]

@michellep I've assigned a milestone, please change if it's inappropriate.

[michellep-basho]

Thanks, Scott. It would be great to have this by 2.1.

[bashopatricia]

Leave open pending discovery. Ping @seemaj