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Alexander Kukushkin authored
Recently released psycopg2 split into two different packages, psycopg2, and psycopg2-binary which could be installed at the same time into the same place on the filesystem. In order to decrease dependency hell problem, we let a user choose how to install psycopg2. There are a few options available and it is reflected in the documentation. This PR also changes the following behavior: * `pip install patroni` will fail if psycopg2 is not installed * Patroni will check psycopg2 upon start and fail if it can't be found or outdated. Closes https://github.com/zalando/patroni/issues/1021