mutt: fix usage validation and help in control script
mutt: fix usage validation and help in control script

The variable name was wrong, and the help didn't make sense because we
were showing the same error message for two different classes of usage
error (non-existent command and wrong number of arguments). Also, we
missed "term" from the list of valid commands.

wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent