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

sh/runscript.sh.in

@@ -4,6 +4,11 @@
 # Copyright (c) 2007-2009 Roy Marples <roy@marples.name>
 # Released under the 2-clause BSD license.
 
+dir_writable()
+{
+	mkdir "$1"/.test.$$ 2>/dev/null && rmdir "$1"/.test.$$
+}
+
 sourcex()
 {
 	if [ "$1" = "-e" ]; then