[WIP] PHP-1107: Additional connection timeout fixes

https://jira.mongodb.org/browse/PHP-1107
This is new behavior, but it's what I would have expected a non-positive timeout to do (block indefinitely). I opted to include 0 here instead of making it an immediate poll (which `select(2)` supports), since I think it's more intuitive and easier to document. When streams connect, we only apply a timeout when the option is > 0. While PHP's own `default_socket_timeout` setting does apply in the absence of a specified timeout, it's probably as good as blocking indefinitely (default value appears to be 60 seconds).