Can't handle screen resolution changes -- X.org 6.8.2 on Mac OS

[Ryan Newton]

When I switch from using my Macbook pro's built-in lcd screen to an
external monitor, X.org doesn't realize that the screen size has
changed.  Thus,  I can only move windows around within a confined
area, even though the screen has become larger.

I installed X.org via fink and am running it simply using
"XDarwin.app".  I'm running in rootless mode, but in full screen mode
the behavior is even worse (the display just goes to hell when I
change resolutions, incorrectly trying to draw at the old resolution).

I looked into using xrandr to change the screen size manually, but I
get an "extension RANDR missing on display ..." error, even when
Xinerama is disabled.

Maybe Xinerama is actually something I could use to fix this... but I
haven't figured out how to configure it yet.....

Does anyone have any ideas on how to work around this?  Or is it known
to work in a newer version?

Thanks for any help,
 -Ryan