That is, those with more than 65520 vertices. Not properly supported for
sw or gl, and glsl isn't rendering properly for some reason (renderdoc
does see the meshes, though, so maybe depth or winding issues).
It now takes a context pointer (opaque data) that holds the buffers it
uses for the temporary strings. If the context pointer is null, a static
context is used (making those uses of va NOT thread-safe). Most calls to
va use the static context, but all such calls have been formatted
consistently so they are easy to find when it comes time to do a full
audit.
