Prototype to test nonblocking file objet:
 - add getblocking() and setblocking() methods to _io._FileIO and all _pyio classes
 - fileio_setblocking() is implemented using fcntl(fd, F_SETFL, flags | O_NONBLOCK) (POSIX only?)
 - BufferedReader.read() uses read1() if the file is blocking

Use test_process.py to test it: this script runs a Python interpreter in a subprocess. It uses select() to check if there is data or not. Eg. type '1+1\n' and then 'exit()\n'. Set PYIO_HAVE_BLOCKING constant to False (in test_process.py) to test the script without io_blocking.patch.

I'm not sure that select() is required, but it doesn't work without it (read() blocks).