i965: Ask the VBO module to actually use VBOs.

Note that this covers the Begin/End rendering path, but not user vertex
arrays (so we can't drop copy_array_to_vbo_array() code).  Improves
performance of isosurf GLVERTEX|TRIANGLES by 16.7506% +/- 4.98934%
(n=20). No difference on openarena (n=10), which was why this was reverted
back in cbde276580.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/drivers/dri/i965/brw_context.c

@@ -781,6 +781,9 @@ brwCreateContext(gl_api api,
       brw_init_performance_monitors(brw);
    }
 
+   vbo_use_buffer_objects(ctx);
+   vbo_always_unmap_buffers(ctx);
+
    return true;
 }