FIX: Fixed basic portability issues

- added missing includes
- renamed ca::ThreadBase::send to ca::ThreadBase::send_unicast to prevent clashes with ::send
- renamed caclient::CaClient::connect to caclient::CaClient::create_connection to prevent clashes with ::connect
- replaced occurences of "/tmp" with tempfile.mkdtemp()
- replaced '/bin/sh' with just 'sh'
- replaced direct invocation of .py files with calls to python with the file as a parameter
- ensured that environment is inherited when running tests
ENH: Added Gnulib portability library
ENH: Added Gnulib and Winsock to compilation process