title: wp_remote_post with file payload
body: <p>I'm attempting to POST a file through <a href="http://core.trac.wordpress.org/browser/tags/3.7.1/src/wp-includes/http.php#L88" rel="noreferrer">wp_remote_post</a>. Unfortunately, any file stream, or file paths (prepended with CURL style @, or not), passed to this function are simply dropped and removed from the payload. </p>
  
  <p>I found a post on <a href="http://lists.automattic.com/pipermail/wp-hackers/2013-January/045105.html" rel="noreferrer">wp-hackers</a>, however, it's extremely hack-ish and error prone. Is there really no way to transmit a file through this function without writing a complete HTTP payload from scratch? </p>
  
  <p>Here's an example code block using CURL style (prepending path with @), if interested:</p>
  
  <pre><code>    $body["attachment[{$i}]"] = "@{$attachment}";
  
      $data = array(
      'body' =&gt; $body,
      'headers' =&gt; array(
          'Authorization' =&gt; 'Basic ' . base64_encode( "user:{$apiKey}" )));
  
  $url = "https://api.someservice.net/{$domain}/endpoint";
  $response = wp_remote_post( $url, $data );
  </code></pre>
  
  <p>Thanks!</p>