Remove timeout callback on errors during connect or request.

Force gc to collect _HTTPConnection object in case of exception (e.g. connection error) without waiting for timeout.
A simple code demonstrates the reference to connection object after connection refused error:
https://gist.github.com/vkosh/4990611
![backref](https://f.cloud.github.com/assets/28398/173672/0e53da3a-7ae4-11e2-9ea2-34abf0f962dc.png)