Connection remains open if InternalError happened during connect()

Imagine following situation:
```python
if conn.closed:
try:
conn = yield from aiopg.connect(dsn)
except psycopg2.InternalError as e:
print("reconnect InternalError ", str(e), type(e))
except psycopg2.Error as e:
print("reconnect error ", str(e), type(e))
```

When connect() raises InternalError (in my case that happens during hstore select request) conn is still points to old connection, but new connection remains open and after some time will emit ResourceWarning about deleting connection object with open _conn.