[plt-scheme] DrScheme lock up bug.

DrScheme seems to have a bug where it'll load but hang right after
starting when using a 90 degree rotated monitor layout.

I was trying to run DrScheme from a fresh 4.2.4 i386 win32 installer
and i kept getting crashes, till i shifted back my monitor to standard
"horizontal" position.
Its been fully replicatable, even halting a running DrScheme by
changing the aspect ratio/turning the screen on the fly and unlocking
it by going horizontal again.
The preference file seems to update everytime any changes to the
screen resolution is made.

The machine currently runs a WinXP sp3 32bit with a 64bit processor
installed and a dual screen setup.
2nd screen is not rotatable.

Hope itll help improve another cool app.