Switch WP_HTTP over to using the mbstring.func_overload helper functions. This change moves the check from within the Streaming-handling function to wrap the individual request, this fixes it for both cURL and Streams and any future changes to the transports which use strlen() on binary data. See #25259 See #16057


git-svn-id: https://develop.svn.wordpress.org/trunk@25348 602fd350-edb4-49c9-b593-d223f7449a82