Spawning risk subtasks
Merged from master
Added OqTaskManager and implemented spawn_risk_task
Made agg_result functional
I discover that the scenario_damage/core_test has been broken for a long time
Several fixes
Fixed a serious bug with the outputdict
Improved the logging
More logging
Renamed subtasks
Merge branch 'master' of github.com:gem/oq-engine into risk-subtasks
Reintroduced a method task_arg_gen in the risk calculators
Improved a docstring
Merge pull request #1436 from gem/risk-subtasks

Better parallelization of the risk calculators
Tasks with fewer assets are submitted first
Merge pull request #1439 from gem/fix-task-ordering

Tasks with fewer assets are submitted first
Merge branch 'master' into ses_collection-scenario