abuild: supporrt for install_if. remove unused 'backup'

abuild.in

@@ -479,12 +479,12 @@ EOF
 	for i in $provides; do
 		echo "provides = $i" >> "$pkginfo"
 	done
-	for i in $backup; do
-		echo "backup = $i" >> "$pkginfo"
-	done
 	if [ -n "$triggers" ]; then
 		echo "triggers = ${triggers#*:}" >> "$pkginfo"
 	fi
+	if [ -n "$install_if" ]; then
+		echo "install_if = $(echo $install_if)" >> "$pkginfo"
+	fi
 
 	local metafiles=".PKGINFO"
 	for i in $install ${triggers%%:*}; do