title: support multipart POST for apachebench?
body: <p>I want to use apachebench (ab) to test file upload performance.
  I have read the manual and can't find a way to achieve my goal.</p>
  
  <p>My goal is try to upload a file by a HTTP Request with POST method and multipart/form-data format.</p>
  
  <p>The ab support "-p POST-FILE", but I only can find the format  key=value&amp;key2=value2</p>
  
  <p>What the post data I want to send is </p>
  
  <p>Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryuUlX4554LPBjInc5</p>
  
  <p>------WebKitFormBoundaryuUlX4554LPBjInc5
  Content-Disposition: form-data; name="file"; filename="411c40d9.jpg"
  Content-Type: image/jpeg</p>
  
  <p>XXXXXXXXXXXXXXX (IMAGE DATA)
  YYYYYYYYYYYYYYYYYYYYYYYYYYYYY</p>
  
  <p>I googled for a while and can't find any related article or way to achieve that.
  I use cURL and it works fine, but I want to do stress testing.
  So I need use ab to achieve that goal.</p>
  
  <p>Any suggestions?</p>