i haven't checked it in yet (the version where all the buttons work)
you should be able to see the render film display though,
but only when you use a 'multifilm' with the relevant ldr/tonemapping parameters.
change your scenefile with the infos i posted in scene file format about the new multiimage film module.
the legacy pbrt film module does'nt know about the required framebuffer and ldr tonemapping.