theora_encode_comment memory ownership inconsistent

the docs in theora.h say that the memory buffer returned in the ogg_packet structure by a call to theora_encode_comment() is owned by libtheora, so the caller should copy and then drop the reference, but this is only true when using libogg2. Under libogg1, the implementation just _ogg_malloc()'s appropriate storage and returns.

There's a comment in the source for this case indicating the caller must free, but of course most people follow the API docs and leak. We need to figure out a way to make this consistent.