MEW 22-12-91

1. Changed 'Dir' procedure in 'Directory file, so that "$.fred.jim", where
   "$.fred" is a file now returns NOT FOUND.

2. Changed 'StoreDirectory' procedure in 'DiscOp' file to deal with 0 length
   files.  Only change was: line 495
    MOVS R3, R3, LSL #8
    MOVEQ  R3, #1:SHL:8
    STR R3, [ R9, #LBASTARTOFFSET ]

   used to be:
    MOV R3, R3, LSL #8
    STR R3, [ R9, #LBASTARTOFFSET ]

3. Changed CDFS_WhereIsFile in file 'SWI'.
4. Changed 'TestDiscKnown' procedure in 'DiscOp'.  Added CD_StopDisc.  This
   is to help the Cumana drive when playing audio.
