[Tremor] RFC: Tremor API changes

[Timothy B. Terriberry]

xiphmont at xiph.org wrote:
> For the record, I second Tim's proposal.  Also, I think we both
> consider this provisional on list feedback.

Since I didn't get any feedback, I've gone ahead and committed the 
changes. See r17374 and r17375 in svn. vorbis_synthesis() got split into 
the original two-argument function and a new 
vorbis_synthesis_trackonly(), which mirrors the libvorbis API.

I did not wind up applying this to lowmem-branch or lowmem-no-byte, 
because, after I actually looked at the code, I discovered those use 
vorbis_dsp_synthesis, which takes a vorbis_dsp_state instead of a 
vorbis_block argument already, so it didn't seem worth adding API churn 
to something that wasn't compatible with libvorbis's API to begin with.

The libogg conversion also included a backport of a number of vorbisfile 
fixes from libvorbis, including several bug fixes. The lowmem branches 
did not get these backports, because their vorbisfile implementation has 
diverged rather farther than trunk's had. If someone really wants them, 
please harass me into at least backporting the bugfixes.