Field interlaced decoding, contributed by Christoph Kuehnel

decoder.c
=========
- Some new defines for DIV
- <decoder_mb_decode> modified: had wrong address offsets for interlaced
- <decoder_mbinter_field> = new function for interlaced
- <get_motion_vector_interlaced> = new function for interlaced motion vector prediction
- <decoder_pframe> modified so that it differs between frame and field prediction

global.h
========
- For field motion prediction MACORBLOCK has new member that is the average of
  field1 and field2 motion vector = <mvs_avg>

xvid.c
======
- For field predicted macroblocks we need new field oriented transfer functions.
  For colour calculations they may only process 4 lines (one field from the colour
  macroblock that is 8x8). So I introduced 4 new function pointers:
  <transfer8x4_copy, interpolate8x4_ ...)

mbcoding.c
==========
- _DEBUG code; index is checked against 64

interpolate8x8.[c,h,asm]
===========================
- New 8x4 functions

mbpredicition.[c,h]
===============
- New function <get_pmv2_interlaced> for interlaced prediciton according to spec

mem_transfer.[c,h,asm]
==============
- New 8x4 function