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.
A ScriptConduit for use with HTML/PRE wrapped Javascript output.
Scripts begin with an html, body and pre tag followed by plain Javascript
without 'execute-in-parent-context' wrapping, but with script-start and
script-end markers.
If this conduit is used the client should direct the output to an iframe
and then poll, looking for new data into the iframe.