Piwik_Http currently sends the client's IP in a spoofed Referer header. We should use X-Forwarded-For.
Piwik_Http currently sets the User-Agent according to the plugin. We should this according to the user's UA, and use Via.
The stream transport uses file_get_contents. For large files, this might exceed PHP's max memory limit.
(In ) fixes #2441, fixes #1869
(In ) refs #2441