Fix for topleft intra prediction edge if we're using a temp dest buffer.

This fixes the final 4 fate tests with -flags +emu_edge. It also removes
a wrong assert().
Fix minor memory overrun on fate-vp9-03-size-196x210.
Modify loopfilter for 16wd to allow operating on 8px edges also.

This prevents memory overruns (or failed assertions) on odd-block image
edges.
Implement flush (for seeking).
Convert printf() to av_log().
Minor changes for codec checklist.