[package] base-files: Add function pi_include the /lib/functions/boot.sh used by preinit, which safely sources files as well as working correctly whether the script using it is a package added to the jffs2 part of a squashfs or built into an image or on some other root filesystem.

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@23099 3c298f89-4303-0410-b956-a3cf2f4a3e73

package/base-files/files/lib/functions/boot.sh

@@ -98,3 +98,16 @@ ramoverlay() {
 	mount -t tmpfs root /tmp/root
 	fopivot /tmp/root /rom 1
 }
+
+pi_include() {
+	if [ -f "/tmp/overlay/$1" ]; then
+		. "/tmp/overlay/$1"
+	elif [ -f "$1" ]; then
+		. "$1"
+	else
+		echo "WARNING: $1 not found"
+		return 1
+	fi
+	return 0
+}
+