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
Fixed a subtle bug in the scenario calculator with duplicate imts
Merge pull request #1437 from gem/distinct-imts

Fixed a tricky bug in the scenario calculator with duplicate imts
Merge branch 'master' of github.com:gem/oq-engine into risk-subtasks
Added a forgotten distinct
Reducing the celery timeout from 30s to 3s
Merge pull request #1438 from gem/celery-timeout

Reducing the celery timeout from 30s to 3s
Reintroduced a method task_arg_gen in the risk calculators
Now the scenario calculator exports a ses_collection too
Improved a docstring
Merge pull request #1436 from gem/risk-subtasks

Better parallelization of the risk calculators