DW:

DW:
 - Running the current code on an older 2.4 cache results in unlink
   errors.  During 2.4 development, we changed the way swap file
   numbers are assigned and stored.  The high 16 bits used to encode
   the SD index number.  There used to be a call to storeDirProperFileno
   here that re-assigned the index bits.  Now, for backwards
   compatibility, we just need to mask it off.