add a new modified sandbox "box"
The original file was pulled from moe (git://git.ucw.cz/moe.git)
by Martin Mares's commit on Sun Jul 29 23:53:56 2012 +0200

The modification is to make it separately compilable and add more option
to specify additional argument to the program. (Please see usage guide)

run `gcc -o box -std=c99 box64-new.c` to compile.