File db.conf, located in the same directory as bigsdb.conf for consistency.
This configuration allow to set another role for the application to connect
to the database than 'apache'. However, this can still be overridden by
parameters from config.xml.

Fixes #286.

Closes #285.

Make sure we don't return null values for non-BIGSdb databases.

Support for fields additional to the group id will require quite a lot
of code. The tables are in place, but we need to get ready for a
release.

They are different each time.