Caqti 0.9.0 release - Compatibility layer for database clients

I made another bugfix release (0.11.1). This only contains one fix, but I think it was important enough, since it could lead to a dead-lock in case there were problems with the database connection.

(On a minor note, I also have a PR to disable testing via opam due to issues with internal dependencies. I expect to re-enable it for the next release.)