Merge pull request #323 from infrastation/develop

add -r/--no_flow_cleanup option to "trema run"
Updated gem dependencies.
Merge branch 'develop' of https://github.com/trema/trema into develop
Drop packet-in if its dest MAC is a reserved MAC.
Fix SetEth*Addr specs to work with Pio::Mac.
Add git to prerequisites (used by gem).