LabPro USB support on Macintosh OSX

The LabPro support now includes USB connections on MacOSX, throught ehLabPro_USB.py module and the LabProUSBMacServer.c server. The server is a relatively trivial IOKit client which connects its stdin and stdout to the out and in USB pipe of the LabPro. Support for other platforms should be easy to develop by anyone who is willing to help, by writing a similar pipe server or by directly talking to the USB from Python.