(PATCH) Install script says it needs /bin/sh but actually requires bash

The install script at http://install.perlbrew.pl starts with
#!/bin/sh
but actually requires bash. It could start with
#!/usr/bin/env bash
However, there is no good reason to require bash, so the following patch makes the install script work using /bin/sh. BTW, the script contains no version info; this patch is against what was downloaded on 5/16/2016:

--- index.html 2016-05-17 01:13:06.860722448 +0000
+++ index.html.NEW 2016-05-17 01:44:53.409322430 +0000
@@ -1,10 +1,12 @@
#!/bin/sh

-if [ "x${PERLBREWURL}" == "x" ]; then
+set -e -u # die if something fails or an undef variable referenced
+
+if [ "x${PERLBREWURL:-}" = "x" ]; then
PERLBREWURL=https://raw.githubusercontent.com/gugod/App-perlbrew/master/perlbrew
fi

-if [ -z "$TMPDIR" ]; then
+if [ -z "${TMPDIR:-}" ]; then
if [ -d "/tmp" ]; then
TMPDIR="/tmp"
else

Start with the install script at http://install.perlbrew.pl and compare it with the supplied patch, focusing on /bin/sh compatibility and unset variables. Verify that the script runs under /bin/sh without requiring bash and that its existing installation behavior is preserved.

Written by the indexing model from the issue text.