With this patch, when a child exits, all of its open file descriptors get
closed immediately. This is necessary to unblock the parent if it is
trying to read from a pipe (connected to the child) before calling
'wait4()'.
Fixes#357.
The 'noux_bash.run' script has become able to present the user with an
interactive bash shell for executing various coreutils programs. It is
still pretty limited, i.e., the environment is not correctly passed to
child processes and pipes are not supported. But bash and coreutils are
operational.