Implement workarounded freopen()

If name is NULL, freopen() returns NULL even if it succeeded.

    new file:   ../io/freopen.c
    modified:   Makefile
    new file:   freopen-1.c
Implement workarounded setmode()

    new file:   ../io/setmode.c
    modified:   Makefile
    new file:   setmode-1.c