Connection Timeout Option for the Ruby Driver

Right now if the Ruby driver tries to set up a connection to a host that is unreachable or nonexistent, the connection attempt appears to last ~30 seconds before timing out.

If possible, it would be nice for the MongoDB Ruby driver to have a configurable connect timeout option. Specifically, we'd like to be able to set a timeout on setting up a connection to a host — not a timeout on socket reads (which is configurable using the :op_timeout option).