Changed the parallelize method to spawn all the tasks at once
Fixed a misprint
Restore concurrent_tasks to its original value (committed a different one by mistake)
Restore a log message removed by mistake
The percentage must be approximated from below to avoid getting a fake 100%
Removed a redundant record_init_stats
Merge pull request #1295 from gem/improve-parallelize

Improve the parallelize distribution
Merge pull request #1296 from gem/sources-done-right

Filter the sources before storing them in the database
Merge branch 'master' of https://github.com/gem/oq-engine into simplify-schema