'List contained items on a node.
Examples
> ls
> ls ../layout'

def do_ls(self, arg):

    path = self.current
    if arg:
        path = self._findPath(arg)
        if (not path):
            return 'No    such    path.'
    l = self._ls(path)
    l = [('%s/' % i) for i in l]
    return self.columnize(l)
