Passes a stream to HTTPUtils to parse

Uploading files was borking with this error:

```
undefined method `each_line' for #<Unicorn::TeeInput:0x007f85abbba188>
/opt/rubies/1.9.3+envato4/lib/ruby/1.9.1/webrick/httputils.rb:312:in `parse_form_data'
/opt/rubies/1.9.3+envato4/lib/ruby/gems/1.9.1/gems/rack_fake_s3-0.2.3/lib/rack_fake_s3/file_store.rb:163:in `store_object'
/opt/rubies/1.9.3+envato4/lib/ruby/gems/1.9.1/gems/rack_fake_s3-0.2.3/lib/rack_fake_s3/server.rb:197:in `do_POST'
/opt/rubies/1.9.3+envato4/lib/ruby/gems/1.9.1/gems/rack_fake_s3-0.2.3/lib/rack_fake_s3/server.rb:74:in `perform'
/opt/rubies/1.9.3+envato4/lib/ruby/gems/1.9.1/gems/rack_fake_s3-0.2.3/lib/rack_fake_s3/server.rb:63:in `call'
```