Two changes, one fix one improvement. Fix: Some agents were not being
logged in the agent_death files as the list was being cleared at each
simulation timestep rather than output period. This has been addressed.
Improvement: env_Sum file now lists the global production rate of each
solute in that output step, across all reactions.
Merge pull request #27 from kalden/AgentDeath_Fix

Agent Death Fix and env_Sum report changes