Add two tests to verify connection resets
They currently fail, because the file descriptor changes while the reset, and this is not properly handled. Therefore conn.block fails on the new connection.
Revert "Move PQsocket() to connection init for better performance"
Storing a copy of the socket file descriptor has the risk of getting out of sync with the socket stored in PGconn. This could happen while conn.reset().
Instead of fixing this, I propose to revert this commit. The performance benefit is not mesurable and it is in a code section where the client is waiting for the server anyways.
Fixes #282 (hopefully)