single: adding support for stereo-pair calibrated cameras

@jbohren I have a concern about this. I have checked the specifications of http://docs.ros.org/api/sensor_msgs/html/msg/CameraInfo.html: for horizontal stereo pairs Tx = -fx · Baseline, Ty = 0 and for vertical ones Tx = 0, Ty = -fy · Baseline. In REEM and REEM-C it is like this.
You are assuming that P[3] and P[7] are in metric units, when they should be in pixel · metric units. I think this line should look like:

leftToRight.setOrigin(tf::Vector3(msg.P[3]/(-msg.P[0])/1000.0, msg.P[7]/(-msg.P[5])/1000.0, 0.0));

Apart from that, in our robots the metric unit in P[3] is meters, not milimeters. There is no convention specified in camera_info documentation. Do you know something more about this? Should it be mm?