tools/dbmaint:

Updated dbmaint tool, since it hasn't been touched/used in a while.
It still works!
db/models:

Added `risklib_version` to OqJob.
db/schema/openquake.sql:

Added `risklib_version` to oq_job.
engine:

Record all software versions in oq_job when the job is initialized.
db/schema/upgrades:

Added upgrades folder and a simple migration script for adding a new
column.
db/schema/load.sql:

Set current revision info on load.
bin/oq_create_db:

Fixed some minor issues in setting up the `revision_info`, which was
interfering with smooth migrations using dbmaint.py.
db/schema/load.sql:

Added a comment to explain the why we are setting the revision_info
when the database is bootstrapped.
bin/oq_create_db:

Don't mess with the revision info when the --tabs-spaces-only option is
selected.
Merge pull request #1232 from larsbutler/record-sw-versions-in-job

Record all OQ software versions in oq_job

[r=matley]