Added PHP version checks.

PHP 5.x is not supported.
PHP < 7.3 may work but has known issues and so is not supported.

setup.php

@@ -43,6 +43,14 @@
 	$database_type_name = "PostgreSQL";
 }
 
+$phpVersionWarning = "";
+
+if (version_compare(phpversion(), '6', '<')) {
+	$phpVersionWarning = "<span class=\"failure\">Versions of PHP below 7.x are not supported, please upgrade.</span><br /><br />";
+} elseif (version_compare(phpversion(), '7.3', '<')) {
+	$phpVersionWarning = "<span class=\"failure\">Versions of PHP below 7.3 may work but have known problems, please upgrade.</span><br /><br />";
+}
+
 $page[ 'body' ] .= "
 <div class=\"body_padded\">
 	<h1>Database Setup <img src=\"" . DVWA_WEB_PAGE_TO_ROOT . "dvwa/images/spanner.png\" /></h1>
@@ -62,6 +70,7 @@
 	{$DVWAOS}<br />
 	<br />
 	PHP version: <em>" . phpversion() . "</em><br />
+	{$phpVersionWarning}
 	{$phpDisplayErrors}<br />
 	{$phpDisplayStartupErrors}<br />
 	{$phpURLInclude}<br/ >