[plt-scheme] member in teaching languages

(member 'B '(B A C)) returns '(B A C) in Intermediate Student with 
Lambda in up to and including 299.27. My next installed version is 
299.100, and from then on, it returns true. Personally, I think that 
true is easier for students to deal with, but the documentation does not 
reflect this change; it still claims that member returns (union false 
list). The change broke my solutions from last year; it must have broken 
what other people have done, so I am a little surprised that I have not 
heard of it before. --PR