Bug#4305: metmail uses non-existent flag in postinst

[Mark Eichin <eichin@cygnus.com>]

> Where's th problem? You can install it as priority 1  (and thus moving

The problem is that the interface is *far* from intuitve.  It needs at
least a sentence or two up top explaining what it's asking about (it
wasn't clear to me until after I'd seen a third viewer show up...)

Remember, many people installing the mime stuff really have *no idea*
what ranking is appropriate (I didn't even know that ranking was
*possible* until I started getting these messages :-) Perhaps it
should just do something by default  (last highest?) and then provide
some tool for configuring them later?