Send the "callerid" field when connecting.

This should be an optional field, but is apparently mandatory in the
core ROS tooling that ships with the Indigo version.

The bug was discovered and fixed by @akru on github.

Fixes #25

src/Ros/Node/RosTcp.hs

@@ -70,7 +70,8 @@ negotiatePub ttype md5 sock =
        case lookup "tcp_nodelay" connHeader of
          Just "1" -> setSocketOption sock NoDelay 0
          _ -> return ()
-       sendAll sock $ genHeader [("md5sum",md5),("type",ttype)]
+       sendAll sock . genHeader $
+         [("md5sum",md5), ("type",ttype), ("callerid","roshask")]
 
 -- |Accept new client connections. A new send buffer is allocated for
 -- each new client and added to the client list along with an action