title: PHP filter_input not working
body: <p>I have a PHP script that shows some server variables, the code is as following :</p>
  
  <pre><code>&lt;?php
  $FILTEREDHOST = filter_input(INPUT_SERVER,'HTTP_HOST');
  $FILTEREDSELF = filter_input(INPUT_SERVER,'PHP_SELF');
  
  $SERVERHOST = $_SERVER['HTTP_HOST'];
  $SERVERSELF = $_SERVER['PHP_SELF'];
  
  var_dump($FILTEREDHOST);
  echo "&lt;/br&gt;";
  var_dump($FILTEREDSELF);
  echo "&lt;/br&gt;";
  var_dump($SERVERHOST);
  echo "&lt;/br&gt;";
  var_dump($SERVERSELF);
  </code></pre>
  
  <p>The result I get is :</p>
  
  <pre><code>NULL
  string(9) "/test.php"
  string(17) "www.mysite.com"
  string(9) "/test.php" 
  </code></pre>
  
  <p>Why  <code>$FILTEREDHOST</code> is returning <code>NULL</code> ?</p>
  
  <p>My PHP version is 5.5.16</p>