* Fixed a memory leak in the curl handlers in which references to callbacks
  were not being removed by `curl_reset`.
* Cookies are now extracted properly before redirects.
* Cookies now allow more character ranges.
* Decoded Content-Encoding responses are now modified to correctly reflect
  their state if the encoding was automatically removed by a handler. This
  means that the `Content-Encoding` header may be removed an the
  `Content-Length` modified to reflect the message size after removing the
  encoding.
* Added a more explicit error message when trying to use `form_params` and
  `multipart` in the same request.
* Several fixes for HHVM support.
* Functions are now conditionally required using an additional level of
  indirection to help with global Composer installations.
