Quoting POSIX[0]:
"Care should be taken, also, to call _exit() rather than exit() if exec cannot be used, since
exit() flushes and closes standard I/O channels, thereby damaging the parent process' standard
I/O data structures. (Even with fork(), it is wrong to call exit(), since buffered data would
then be flushed twice.)"
[0]: http://pubs.opengroup.org/onlinepubs/009695399/functions/vfork.html
1) no need to include sys/stat.h
2) remove the enum which just added a layer too thick on this simple
program
3) argc-style, other style
4) weprintf instead of enprintf, then save the error-message of
execvp before and return the proper status.
5) write consistent "not reached" comment.
