add uninstall script

utilities/extra/uninstall.sh

@@ -0,0 +1,20 @@
+#!/bin/sh
+extracted_path=/home/owner/Downloads/minetest
+mnf_name=install_manifest.txt
+customDie() {
+    echo
+    echo "ERROR:"
+    echo "$1"
+    echo
+    echo
+    exit 1
+}
+if [ ! -f "$extracted_path/$mnf_name" ]; then
+    customDie "$extracted_path/$mnf_name is missing, so $0 cannot continue."
+fi
+
+
+cd $extracted_path || customDie "* cannot cd $extracted_path."
+echo "- about to run 'sudo xargs rm < $mnf_name'..."
+sudo xargs rm < $mnf_name
+# as per http://irc.minetest.net/minetest/2015-08-06