use a wrapper for install for Darwin

scripts/install

@@ -0,0 +1,10 @@
+#!/usr/bin/env bash
+# This file is part of the OpenADK project. OpenADK is copyrighted
+# material, please see the LICENCE file in the top-level directory.
+
+if [ -z "$(which ginstall 2>/dev/null)" ];then
+	/usr/bin/install "$@"
+else
+	ginstall "$@"
+fi
+