Add support for HEAD method in cURL driver (rfc2616)

Adding the missing HEAD method in cURL driver.
This is a GET method which doesn't return a message body.

From the RFC : 
_The HEAD method is identical to GET except that the server MUST NOT return a message-body in the response. The metainformation contained in the HTTP headers in response to a HEAD request SHOULD be identical to the information sent in response to a GET request. This method can be used for obtaining metainformation about the entity implied by the request without transferring the entity-body itself. This method is often used for testing hypertext links for validity, accessibility, and recent modification._