between cabextract.c and fdi.c
- reminders to eliminate global variables (for multithread
  compatibility)
- remove struct fdi_cab: due to the nature of the FDI API, we cannot
  preload all the cabinets; this appears to obviate the need for struct
  fdi_cab
- "oppress" (that is, do not process) partial files which were
  continuations from another cabinet
- more than one partial file can exist in a single cabinet (how!?) --
  so move the partial file notification (and "oppression" that goes with
  it) into the loop that iterates through files