Adding a quotefmtinstall call to respondcmderror (the way it is done
in libauth too), since it is using a "%q" verb.


Before that I got messages like

	unknown control message: "%q% %q% %q% %q%"

when trying to partition a usbsfs data file, since usbsfs apparently
doesn't know the `part' command.


With the patch it prints
	unknown control message: "part 1 2 33"