`define-minor-mode' makes erroneous docstrings.

[Luc Teirlinck]

The docstrings provided by `define-minor-mode' are wrong for many
minor-mode variables.  They _automatically_ say that setting the
variable directly has no effect.  I believe that this is wrong for the
majority of minor modes.

For global minor modes, setting the variable buffer locally is often
useful, like for column-number-mode.  For local minor modes, you can
enable them globally by setting the default-value of the variable.

As an example here is what you get from `C-h v column-number-mode'.
It is definitely wrong, you can set it directly and buffer locally.
It works.

  column-number-mode's value is t
  Local in buffer *info*; global value is nil

  Non-nil if Column-Number mode is enabled.
  See the command `column-number-mode' for a description of this minor-mode.
  Setting this variable directly does not take effect;
  use either M-x customize or the function `column-number-mode'.

  You can customize this variable.

  Defined in `simple'.