Created update_db_version for opening older versions of the Scenario.
Migrations should include the record of the DB as it is AT THE END of the migration, then intended state.  This was fixed.
Not relying on scenario_filename until we split databases.
Comment on Foreignkeys
The "ratio" output variable in infection-monitor -- which was intended to be a rough version of EDR -- has been taken out of the tests, since there is currently no field in the database for specifying the width of the sliding time window over which EDR is computed.
Fixed field name typo
Added support for Piecewise and Histogram.  Rearranged equation_type ordering.
Added migration for previous commit
Merge remote-tracking branch 'origin/master'
Merge branch 'migrations'
All output variables in infection-monitor now default to being reported daily. Module loader now activates the full-table-writer whenever the state-table-writer *isn't* active. That makes the automated test suite work, but we will need some extra database fields to properly exercise control over which files are/aren't output from the simulator. All tests in the airborne spread section of the automated test suite now pass.
Merge branch 'master' into SQLite