fix typos
Replica should ignore out-of-date DecisionHints

Defensively check for slotNum usefulness before applying the
DecisionHint. Otherwise, if we got an old duplicate or a mis-sent
DecisionHint it could do something nasty.
Merge pull request #58 from snatchev/fix-typos

fix typos
getRandomMember returns Try instead of Option

Try maps much more cleanly to what getRandomMember is hoping to do. This
setup models failure a little more gracefully, and will be useful in
rebuilding some of our catchup logic.
Merge pull request #73 from clinedome-work/ignore-old-decisionhints

Replica should ignore out-of-date DecisionHints
Merge pull request #74 from clinedome-work/getrandommember-to-try

getRandomMember returns Try instead of Option