Respond with the same headers as we did before, if caching is disabled.

includes/datastream.inc

@@ -191,6 +191,7 @@ function islandora_view_datastream_cache_check(AbstractDatastream $datastream) {
  *   The datastream being viewed/downloaded.
  */
 function islandora_view_datastream_set_cache_headers(AbstractDatastream $datastream) {
+  if (variable_get('islandora_use_datastream_cache_headers', TRUE)) {
     // Force cache revalidation.
     header('Expires: Sun, 19 Nov 1978 05:00:00 GMT');
     $cache_control = array();
@@ -208,6 +209,11 @@ function islandora_view_datastream_set_cache_headers(AbstractDatastream $datastr
       header("Etag: \"{$datastream->checksum}\"");
     }
   }
+  else {
+    header_remove('Cache-Control');
+    header_remove('Expires'); 
+  }
+}
 
 /**
  * Get the human readable size of the given datastream.