apt-selection: order contrib before non-free*

Components are ordered “main contrib non-free” almost everywhere, let's
use the standard order here too. There should be no functional changes.

Note: This controls the sources.list file used during the build, but
doesn't control “deb cdrom:” lines in sources.list during or after
installation, which are the result of running apt-cdrom (which sorts
components alphabetically, see its pkgCdrom::ReduceSourcelist function).

tools/apt-selection

@@ -45,12 +45,12 @@ options=" -q -o Dir::State::status=$APTTMP/$THIS_PKGSET/status \
 		  -o Acquire::Languages=none"
 
 sections=main
-if [ "${NONFREE:-0}" != "0" ] || [ "${EXTRANONFREE:-0}" != "0" ] || [ "${FORCE_FIRMWARE:-0}" != "0" ]; then
-	sections="$sections $NONFREE_COMPONENTS"
-fi
 if [ "${CONTRIB:-0}" != "0" ]; then
 	sections="$sections contrib"
 fi
+if [ "${NONFREE:-0}" != "0" ] || [ "${EXTRANONFREE:-0}" != "0" ] || [ "${FORCE_FIRMWARE:-0}" != "0" ]; then
+	sections="$sections $NONFREE_COMPONENTS"
+fi
 
 # Check for the necessary dirs and files ...
 if [ ! -d "$APTTMP/$THIS_PKGSET/apt-state/lists/partial" ]; then