ge of directory when removing
    	directories from the stack, so only the stack is manipulated.
    
    Arguments:
      +N	Removes the Nth entry counting from the left of the list
    	shown by `dirs', starting with zero.  For 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.