New build_style: "fetch" to only fetch files and copy them to ${wrksrc}.

This is based on the first approach by chneukirchen.

common/build_style/fetch.sh

@@ -0,0 +1,9 @@
+# fetch build_style: fetches and copies files to ${wrksrc}.
+
+do_extract() {
+	mkdir -p ${wrksrc}
+	for f in ${distfiles}; do
+		curfile=$(basename "${f#*>}")
+		cp ${XBPS_SRCDISTDIR}/${pkgname}-${version}/${curfile} ${wrksrc}/${curfile}
+	done
+}