Fixed Issue ros/roslisp#12

For use-case 1:
When subscribing to oneself, subscribers do not wait for answer to send-tcp-header because it would otherwise deadlock. This is applicable because the answer has always been ignored anyway. Additionally, we know the md5 sums to match because we are the same node. Finally, in case of self-subscription publisher do not send response to received tcp-header.

For use-case 2:
When subscribing to oneself, subscribers do not send an xml-rpc to avoid a deadlock. Instead, they directly call |requestTopic| on themselves.
:) Great function name...