As we dn't export constants for TCSANOW, etc., zero makes a good "don't
care" param, and now it will work also under Android Bionic and any other
libc.
Also provides setraw() function from "tty" module (which in CPython is
implemented in Python). The idea here is that 95% of "termios" module usage
is to set raw mode to allow access to normal serial devices. Then, instead
of exporting gazillion termios symbols, it's better to implement it in C,
and export minimal number of symbols (mostly baud rates and drain values).
