[merge request] command related minor improvements

[Teika Kazura <teika lavabit com>]

Hi. Please merge my branch. 

* In an interactive call of `call-command', it used to print an
  errror message if you cancel it with esc key. Now it doesn't any more.
  This will please DM German. (And this year's Ichiro's performance? > dmg)
* New fuction 'report-commands' is defined. (You can use it for
  tab-completion in interactive use of 'call-command' Jeremy may be 
  pleased.)
* Command doc minor revision. Dropped outdated and unused features
  in command definition.

Regards,
Teika (Teika kazura)