Override default maxSockets to Infinity

Closes #41
Its a good idea, but in node 0.10 there is only one option when constructing the Agent: https://github.com/joyent/node/blob/v0.10.31-release/lib/http.js#L1229

For now I vote keep it as is, in node 0.11 if someone needs to change any of these options they still can