Update files to use global $referrerurl variable

If possible, capture the referring URL to use in links to static website pages. This way when coming from a distributed HPR website and not hackerpublicradio.com, clicking on a page link will return you to the original domain.

ini/credentials.php

@@ -20,4 +20,14 @@ $naughty_stings_file = '/path/to/strings.txt';
 $justification_file = '/path/to/justification.txt';
 # Read more: http://vidiame.com/php/how-to-block-multiple-ip-addresses-using-php
 
+# The $referrerurl is used for links to pages from the orginating HPR site.
+$referrerurl = $baseurl;
+session_start();
+if ($_SESSION['referrerurl']) {
+	$referrerurl = $_SESSION['referrerurl'];
+}	
+else if ($_SERVER["HTTP_REFERER"] && !str_starts_with($_SERVER["HTTP_REFERER"], $hubBaseurl)) {
+	$_SESSION['referrerurl'] = $_SERVER["HTTP_REFERER"];	
+	$referrerurl = $_SERVER["HTTP_REFERER"]; 
+}
 ?>