Added NLnet logo on request

includes/sponsorinfo.php

@@ -2,6 +2,7 @@
     CAcert operations are sponsored by
     <a href="http://www.bit.nl/" target="_blank"><img class="sponsorlogo" src="/images/bit.png" alt="[BIT logo]" border="0"></a>
     <a href="http://www.tunix.nl/" target="_blank"><img class="sponsorlogo" src="/images/tunix.png" alt="[TUNIX logo]" border="0"></a>
+    <a href="http://www.nlnet.nl/" target="_blank"><img class="sponsorlogo" src="/images/nlnet.png" alt="[NLnet logo]" border="0"></a>
     <a href="http://www.sonance.net/" target="_blank"><img class="sponsorlogo" src="/images/sonance.png" alt="[Sonance logo]" border="0"></a>
     <a href="http://www.openarchitecturenetwork.org/" target="_blank"><img class="sponsorlogo" src="/images/oan.png" alt="[OAN logo]" border="0"></a>
   </div>