nsIFastLoadService Interface

 Return true if aURISpec identifies a muxed document in the FastLoad
 file, false otherwise.

boolean hasMuxedDocument(in string aURISpec)

 These methods associate a URI object with its spec, for faster select
 using the object pointer as a key, rather than the spec string.  The
 selectMuxedDocument method returns the previously selected URI object,
 in case a caller needs to reselect the previous after muxing data for
 a given URI synchronously.  For the non-blocking or "asynchronous" i/o
 case, the caller must select the source URI from the FastLoad multiplex
 before writing a new burst of data parsed from the slow-loaded source.

 Clients of inputStream and outputStream should try to demultiplex data
 from the input stream only if fastLoadService->StartMuxedDocument(uri,
 urispec, NS_FASTLOAD_READ) succeeds.  If StartMuxedDocument fails with
 NS_ERROR_NOT_AVAILABLE, callers should slow-load the documents, muxing
 their data to the current output stream.

void startMuxedDocument(in nsISupports aURI, in string aURISpec, in PRInt32 aDirectionFlags)