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

Built from https://develop.svn.wordpress.org/trunk@25348


git-svn-id: http://core.svn.wordpress.org/trunk@25310 1a063a9b-81f0-0310-95a4-ce76da25c4cd