add stdbuf-like capabilities to dcc to assist testing student code

[andrew-taylor]

No description provided.

[Dylan-Brotherston]

stdbuf(1) uses LD_PRELOAD, this can conflict with tools like valgrind and only libraries that check for this modification will be affected. Using a set of PTYs to trick isatty(3) should have the same effect and be more portable to other languages/libraries.

[Dylan-Brotherston]

I am thinking this should be implemented in autotest, not dcc, as this is expected/standard behaviour.
Autotest shouldn't be giving programs any idea they aren't being run directly.