Now that we have mc_channel_number stashed in the tag_info after
simulation, picking up this from the metadata during RHadron
second-stage simulation.  Fixing a 'feature' in the metadata accessor
function, since we store the float directly instead of storing the
number as an array.


Former-commit-id: fe142b80b49e3cd6bc6f624f1592a55697bfad52