sfeed_update: if baseurl is empty then use the path from the feed by default

Feeds should contain absolute urls, but if it does not have it then this makes
it more convenient to configure such feeds.

sfeed_update

@@ -84,11 +84,17 @@ feed() {
 	curjobs=$((curjobs + 1))
 
 	(name="$1"
-	filename="$(printf '%s' "$1" | tr '/' '_')"
 	feedurl="$2"
 	basesiteurl="$3"
 	encoding="$4"
 
+	# if baseurl is empty then use the path from the feed by default.
+	if [ "${basesiteurl}" = "" ]; then
+		host="${feedurl##*://}"
+		basesiteurl="${feedurl%%://*}://${host%/*}/"
+	fi
+
+	filename="$(printf '%s' "${name}" | tr '/' '_')"
 	sfeedfile="${sfeedpath}/${filename}"
 	tmpfeedfile="${sfeedtmpdir}/${filename}"