limit number of concurrently executing machines
correctly handle missing database backend
dynamically configure alembics database connection
proper script to update the database layout for the file-type bug, #347
sqlite support for file-type migration
use the correct exception class
Message whatever
Imports ordered
Comment whatever
Added note about dynamic configure alembic migration to documentation
Renamed migration
More descriptive name
mysql support for the extend-file-type database migration
future imports have to be first
typo in pg driver name
Merge branch 'master' into sanity

Conflicts:
	docs/book/src/installation/upgrade.rst
Revert "strip off the end of the file-type string until there is a better fix, #347"

This reverts commit b1c9a22c04d560795d211886cdc5c06a5221b21c.
More comments
Changed database library to reflect last migration schema
Added an error if you try to run on a wrong db schema release