added suppoer for quicktime v210 uncompressed 10bit yuv files.
Thses are generated by DVC video diskstores.

I also tidied readyuv.c a little.

Perhaps its time to change to the file structure. we could put
all the image conversion and maniputation tools in
/sys/src/cmd/image/ and  /386/bin/image/

resample and crop should probably go in there too.

this would also require changes to nedmail, and page but
I think thats all.

my 2¢ worth.

-Steve