Make checks for writable directory posix compliant

Reported-by: Maxim Kammerer <mk@de.su>
X-Gentoo-Bug: 398931
X-Gentoo-Bug-URL: http://bugs.gentoo.org/show_bug.cgi?id=398931

init.d/keymaps.in

@@ -63,7 +63,7 @@ start()
 	fi
 
 	# Save the keymapping for use immediately at boot
-	if [ -w "$RC_LIBEXECDIR" ]; then
+	if dir_writable "$RC_LIBEXECDIR"; then
 		mkdir -p "$RC_LIBEXECDIR"/console
 		dumpkeys >"$RC_LIBEXECDIR"/console/keymap
 	fi