Identifiers in syntax-rules can't be shadowed by local variables

[jcubic]

Recent change deleted the code that checks if identifiers have values in scope. The fix was needed for SRFI-210 with identifier bind from let-values was also bind function in SRFI.

But it should not work this way according to StackOverflow it should work this way:

1. The literal does not have a binding at the point of macro definition, and also does not have a binding at the point of macro
2. The literal has a binding at the point of macro definition, and also has the same binding at the point of macro usage.

So there is a need to wait for #172.

This example should not work:

(define-syntax if+
  (syntax-rules (then else)
    ((_ test then expr1 else expr2) (if test expr1 expr2))))

(let ((else #f) (x 10))
  (print (if+ (even? x) then (/ x 2) else (/ (+ x 1) 2))))

But this should:

(define-syntax if+
  (syntax-rules (then else)
    ((_ test then expr1 else expr2) (if test expr1 expr2))))

(define else #f)
(let ((el_se #f) (x 10))
  (print (if+ (even? x) then (/ x 2) else (/ (+ x 1) 2))))