[Xmonad] How do I know if Xinerama's working?

[Bruce Stephens]

I've just built X11-extras and xmonad, largely without incident, and
Xinerama seems not to be working: when I create an xterm, it spans
both screens.

Is that to be expected?  I was expecting each screen to contain its
own workspace.

There's no problem with my X.org setup in general: I have a
libXinerama.so.1, and (for example) ion3 links against it and seems to
use it.

(xmonad doesn't link against it, according to ldd, but I'm not sure
whether I should expect it to or not.)