avformat: attachments should still be treated as tracks. this fixes [8c5a9c72]

audiofilters: Do not try to insert user audio-filters when our target is SPDIF. We currently have no way to apply any of our filters to the encoded signal.

Moreover, use a function instead of a macro (like in 0.9-branch)
Partially cherry picked from commit 73ab1cd94773956e463009088bf5f477cec1ae80

And only fonts so far.

Do not move an already rendered subtitle.

It will allow detecting stupid typos.

configure: Use fno-omit-frame-pointer with --enable-release on Mac OS X, as we are collecting crash log.

Our real demux is incomplete and crashes avcodec. The avformat demux works, so i say we use it until someone fixes this thing.

I have updated spu_RenderSubpictures and subpicture_region_t->pf_pre_render/pf_update_regions.

It now requires source format instead of scaling parameters.

Yes this creates a 'useless' picture copy per region, but it is
currently needed.

It is useless to wait for the first subtitle.