Add note on excluding content-length header from DELETE requests

src/Curl/Curl.php

@@ -265,6 +265,14 @@ class Curl
 
         $this->setUrl($url, $query_parameters);
         $this->setOpt(CURLOPT_CUSTOMREQUEST, 'DELETE');
+
+        // Avoid including a content-length header in DELETE requests unless there is a message body. The following
+        // would include "Content-Length: 0" in the request header:
+        //   curl_setopt($ch, CURLOPT_POSTFIELDS, array());
+        // RFC 2616 4.3 Message Body:
+        //   The presence of a message-body in a request is signaled by the
+        //   inclusion of a Content-Length or Transfer-Encoding header field in
+        //   the request's message-headers.
         if (!empty($data)) {
             $this->setOpt(CURLOPT_POSTFIELDS, $this->buildPostData($data));
         }