glretrace: Silence NVIDIA's "Buffer detailed info:".

Merely informative.
gltrace: Ensure GL_ARRAY_BUFFER is unbound before emiting fake gl*Pointer() calls.

When tracing, just before every drawcall, ApiTrace inserts gl*Pointer()
calls into the stream on attributes it detected as resident in user-mem
(instead of in a VBO).

ApiTrace wasn't inserting a glBindBuffer(GL_ARRAY_BUFFER, 0) and
glBindBuffer(GL_ARRAY_BUFFER, prevBuf) around those auto-generated
calls.  Thus, it misrepresented pointers as huge offsets into the
currently bound VBO.

Thanks to idinev for spotting and diagnosing this issue.  This achieves
the same result as idinev's fix in issue #222, but from the trace side.