BLIOVLSUS
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  Function : Suspend overlay manager operations

  Syntax   : BLIOVLSUS(niValue)

  Return   : None

  This function shuts down the overlay manager. Depending on the level of
  shutdown required, the overlay manager will free up some or all of the
  system resources which it is using. The numeric values 1 through 3 are
  valid parameters, and the system resources freed for each are as
  follows:

  1   Closing all open overlay files, freeing up the DOS handles.
  2   As (1) above, plus freeing of the EMS/XMS used for the overlay cache
  3   Freeing ALL resources used by the overlay manager including the
      overlay pool.

  When the overlay manager is resumed using the BLIOVLRES() function, it
  will attempt to reallocate the same resources it had before. If it is
  unable to reallocate an overlay area, then the program will terminate
  with a Blinker error 1216, 'Overlay manager unable to resume'. If the
  overlay area is reallocated successfully, but there are no resources
  available for the overlay cache, then execution will continue without
  caching of overlays.

  Note: this routine must be called from the root, as the overlay manager
  will be inactive on return from this call until a call to BLIOVLRES() is
  made.