fix halt wrapper so it is sysvinit compatible

This makes the halt wrapper sysvinit compatible. It ignores several
command line switches which are not currently implemented; however,
those can be implemented if we need to do so.

This fixes https://github.com/openrc/openrc/issues/146.

scripts/halt.in

@@ -1,3 +1,24 @@
 #!@SHELL@
 
-exec @SBINDIR@/openrc-shutdown --halt "$@"
+option_arg=
+poweroff_arg=
+while getopts :nwdfiph opt; do
+	case "$opt" in
+		n) ;;
+		w) poweroff_arg=--write-only ;;
+		d) option_arg=--no-write ;;
+		f) ;;
+		i) ;;
+		p) poweroff_arg=--poweroff ;;
+		[?]) printf "%s\n" "${0##*/}: invalid command line option" >&2
+		exit 1
+		;;
+	esac
+done
+shift $((OPTIND-1))
+
+if [ -z "${poweroff_arg}" ]; then
+	poweroff_arg=--poweroff
+fi
+
+exec @SBINDIR@/openrc-shutdown ${option_arg} ${poweroff_arg} "$@"