[plt-scheme] DrScheme ate my CPU

I hadn't really noticed this for a while, but since compiling
205.3-cvs1oct2003, DrScheme routinely grabs almost 90% CPU usage for up
to half a minute when switching to one of its windows, clicking around
the editor, opening a new window, etc.

SirMail is less painful, the included games run mostly fine, and
web-server-text doesn't ever seem to take much CPU time.

I'm running linux, X 4.3 with accelerated drivers, and compiled MrEd
with Xft support.  Is the issue specific to this platform?

Thanks,

Daniel