example: `popd +0'
    		removes the first directory, `popd +1' the second.
    
      -N	Removes the Nth entry counting from the right of the list
    		shown by `dirs', starting with zero.  For example: `popd -0'
    		removes the last directory, `popd -1' the next to last.
    
    The `dirs' builtin displays the directory stack.
    
    Exit Status:
    Returns success unless an invalid argument is supplied or the directory
    change fails.