(PECL pecl_http:0.10.0-1.5.5)
http_send_content_type — Send Content-Type
Send the Content-Type of the sent entity.
Note: This function is supposed to be used in conjunction with http_send_data(), http_send_file() 和 http_send_stream().
the desired content type (primary/secondary)
如果成功则返回 TRUE，失败则返回 FALSE。
Raises an E_WARNING when the content_type doesn't seem to contain a primary and a secondary part.