- When sending a request using HttpOpenRequest/HttpSendRequest, send the
   User-Agent header; fixed the Accept and the Referer header handling to
   really work.
 - Fixed bug in the HTTP_ProcessHeader: when a second value was supposed to be
   added to an existing one, the buffer was reduced to be 1 char long instead
   of being expanded, due to the precedence rules of the operator '?'.
 - Added support for opening URLs that redirect to a different place.