Recognize content type by temp filename, fix memory leaks

[smoskalenko]

With this MR:

• On POST() action, content type of the uploaded file will be recognized by $_FILES['tmp_name']
• On GET() action , content type of original file will be recognized by original cached filename

In both cases ContentType::byFilenam() will be used which internally call finfo::file method, instead of finfo::buffer (which has a memory leaks)

[Magomogo]

Thanks!