INT 21 - DOS 3.3+ - SET HANDLE COUNT
        AH = 67h
        BX = size of new file handle table for process
Return: CF clear if successful
        CF set on error
            AX = error code (see AH=59h)
Desc:   adjust the size of the per-process open file table, thus raising or
          lowering the limit on the number of files the caller can open
          simultaneously
Notes:  if BX <= 20, no action is taken if the handle limit has not yet been
          increased, and the table is copied back into the PSP if the limit
          is currently > 20 handles
        for file handle tables of > 20 handles, DOS 3.30 never reuses the
          same memory block, even if the limit is being reduced; this can lead
          to memory fragmentation as a new block is allocated and the existing
          one freed
        only the first 20 handles are copied to child processes in DOS 3.3
BUG:    the original release of DOS 3.30 allocates a full 64K for the handle
          table on requests for an even number of handles
SeeAlso: AH=86h