bug#3108: 23.0.92; 2C-command: missing arglist

1. C-h f 2C-command shows this:
 
2C-command is an interactive autoloaded keymap in `two-column.el'.
 
It is bound to <f2>, C-x 6.
 

Not documented.
 

2. In Emacs 22, it shows this:
 
2C-command is an interactive autoloaded keymap in `two-column'.
It is bound to <f2>, C-x 6.
[Missing arglist.  Please make a bug report.]
 
Not documented.
 

Emacs 22 is more correct here, since the arglist is missing.  Even if
there is no doc string, we should show the signature.
 

In GNU Emacs 23.0.92.1 (i386-mingw-nt5.1.2600)
 of 2009-03-30 on SOFT-MJASON
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (3.4)'