conn.changeUser should eject conn from pool

[dougwilson]

When a connection from the pool does .changeUser, it should be ejected from the pool such that the user does not end up in a case where some connections have different contexts.

[memelet]

I have a question about this: I want to use the pool for a multi-tenant app. We have a database per tenant running on a single database (cluster). I was looking forward to using changeUser to select the database as per the tenant making the request. But does this commit mean that if use changeUser I essentially no longer get the benefit of connection pooling? If so, why not just reset the connection when it is returned to the pool?