Re: [Libguestfs] [PATCH] mllib: check for executable existance in run_command (RHBZ#1362357)

run_command uses Unix.create_process which forks a child process, and executes execve: the latter fails when the executable does not exist, triggering the exit which, in older OCaml versions [1], also runs the at_exit handlers. Since there is not much that can be done to avoid this on the OCaml side, to keep run_command working also in older OCaml version then manually search for the existance of the given executable, exiting with code 127 (as a shell does) in this case. [1] http://caml.inria.fr/mantis/view.php?id=7209