This adds a new method launchWithFile on nsIMIMEInfo which takes care of opening
the selected (preferred or default) application on the mime info with a
specified document. defaultDescription is now readonly, and defaultApplication
no longer available.
This also removes the clone method which was unused in the entire tree.
course of action, move the "neverAsk" information from prefs back to
mimeTypes.rdf, remove the "Reset" button from helper app prefs, set up a way to
select "use default OS helper" for a given type. Patch by Bill Law
<law@netscape.com> and Philip K. Warren <pkw@us.ibm.com>, r=biesi, sr=bzbarsky,
what passes for moa in helper apps=bzbarsky.