[plt-scheme] Printing structs in 206

I just upgraded to 206 and got somewhat confused
when I found out that the parameter PRINT-STRUCT
now defaults to #f, which means that display doesn't
print the contents of structs even in the presence
of a newly made inspector.

Why was it changed? I often find it convenient to
use display when debugging.

Anyways, I suggest adding another checkbox to the
printing section in the language details window.

-- 
Jens Axel Søgaard