Terminate connection to database

[alex-dukhno]

Hi there!

Thanks for the rust-postgres is a cool crate 😄

I am building PostgreSQL compatible database and using synchronous Client in my integration tests.
I am starting the server in separate thread and facing the problem that I can't terminate connection with Client.
I think it's good idea to send terminate message when dropping Client that is not closed. WDYT?

[sfackler]

This is normally done by the connection when the client handle drops, but that doesn't currently happen in the synchronous client due to how its constructed. Should be fixable.