bound variables get stripped incorrectly

[felix winkelmann]

Matthew Flatt reports:

The following program prints a gensym in v4.7.0 and 4aaea216cc9887, but I think it should print the symbol 'x:

 (define-syntax c 
   (syntax-rules () 
     [(_) 
      (let ([x 10]) 
        (let-syntax ([z (syntax-rules ()
                          [(_) (quote x)])])
          (write (z))
          (newline)))]))

 (c)

I wrote the example because I'm suspicious of "compiler.scm" treating ##core#quote' and ##core#syntax the same. Maybe ##sys#strip-syntax in "expand.scm" is supposed to do different things in quote and syntax mode; the comment "if se is given, retain bound vars" in ##sys#strip-syntax` suggests that it had two modes at some point in the past.