openopc: new package

"OPC (OLE for Process Control) toolkit designed for use with Python"

This package contains a python module (OpenOPC) and a command line
client (opc). The OpenOPC Gateway Service for Windows is also copied to
$out, for reference.

It only works with python2.7 (not python3.x), so I'm not adding it to
python-packages.nix.

Also add needed dependency, python-pyro3, a distributed object
middleware for Python (IPC/RPC).

http://openopc.sourceforge.net/