nsIZipReaderCache Interface

 Returns a (possibly shared) nsIZipReader for an nsIFile.

 If the zip reader for given file is not in the cache, a new zip reader
 is created, initialized, and opened (see nsIZipReader::init and 
 nsIZipReader::open). Otherwise the previously created zip reader is 
 returned.

 @note If someone called close() on the shared nsIZipReader, this method 
       will return the closed zip reader.

nsIZipReader getZip(in nsIFile zipFile)

 Initializes a new zip reader cache. 
 @param cacheSize - the number of released entries to maintain before
   beginning to throw some out (note that the number of outstanding
   entries can be much greater than this number -- this is the count
   for those otherwise unused entries)

void init(in unsigned long cacheSize)