Changes for Version JM 5.0d to JM 5.0c
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added POC - changes delimited by #ifdef USEPOC
reference pictures need their pocs stored somewhere??


specifically, image parameters now available both at encoder and decoder are

img->frame_num
img->toppoc   	//poc of topfield  and frame
img->bottompoc  //poc of bottom field

encoder uses toppocs  0,2,4,6,8,...


if InterlaceCodingOption = 0 (ie, frame coding) then bottompoc = toppoc
otherwise bottompoc = toppoc+1


decoder is not yet fully compliant, but it does handle the output of the encoder.

sequence parameters and picture parameters are sent in the slice header.  
This will change once the high level syntax is in place.

Things yet to be removed from the slice header include...
tr
pstruct
image size
etc.
