An interface to allow us to plug alternative FileUpload components into DWR,
and more specifically, to plug in a null implementation if file commons
file-upload.jar is not available on the classpath.
author: Joe Walker [joe at getahead dot ltd dot uk]
Process an inbound request into a set of name/value pairs where the
values could be file uploads.
Parameters: req - The request to parse A map of the fields in the input request throws: ServerException - If there is an IOException while reading the request