bug#8857: display-buffer attempt to pop-up frame in batch mode causes "Unknown terminal type" error

[Glenn Morris]

In addition I still think it might be worth explicitly making
display-buffer a no-op in batch mode, unless someone can think of
something it can actually do in such cases. I think this could only be
by side effect. Eg, can it run hooks, and can those hooks be expected to
do anything when there isn't actually a display?

If not then it seems simpler and more efficient to not even try
displaying buffers in batch mode (and less confusing, since it can give
unclear errors trying to do something that cannot work).