Description:
------------
When CURLOPT_HTTPHEADER is called more than once on the same curl handle, 
php/curl does not free the memory of the previous header data.

Similar to bug 63859.

Test script:
---------------
<?php

  $ch = curl_init();

  echo memory_get_usage(), "\n";

  for ($i = 0; $i < 10000; $i++)
  {
    curl_setopt($ch, CURLOPT_HTTPHEADER, [ "SOAPAction: getItems" ]);
  }

  echo memory_get_usage(), "\n";

  curl_close($ch);

  echo memory_get_usage(), "\n";