NAME
        OpenIFF -- prepare an iffhandle to read or write a new iff stream.
                   (V36)

   SYNOPSIS
        error = OpenIFF(iff, rwMode);
        D0              A0   D0

        long openiff(struct iffhandle *, long);

   FUNCTION
        Initializes an iffhandle structure for a new read or write. the
        direction of the I/O is given by the value of rwMode, which can be
        either IFFF_READ or IFFF_WRITE.

        As part of its initialization procedure, OpenIFF() calls the client-
        supplied stream hook vector. The iffstreamcmd packet will contain
        the following:

                sc_Command:     IFFCMD_INIT
                sc_Buf:         (Not applicable)
                sc_NBytes:      (Not applicable)

        This operation is permitted to fail. DO NOT write to this structure.

   INPUTS
        iff - pointer to iffhandle structure. starting with v39, this may be
              NULL, in which case IFFERR_NOMEM is returned.
        rwMode - IFFF_READ or IFFF_WRITE

   RESULT
        error - contains an error code or 0 if successful

   SEE ALSO
        closeiff(), initiff(), <libraries/iffparse.h>