Clients are not reusable. This changes the client to raise errors whenever you try to reconnect a client that's already been used. They're cheap to create: just instantiate a new one (or use the pool) 😉.
Closes#1352
integration tests could now be started in binary mode
some tests are executed in text mode anyway, they are currently not
compatible with binary mode or prepared statements at all
(f.e. multiple statements in one query)