rebirth: relibprebirth: Fix < and >

* build-aux/bootstrap/rebirth/relibprebirth.scm (<, >): Reverse
    comparisons.  This is quite the embarassing mess-up.  It appears that it
    was only used in one place, and so I did not notice the problem until I
    began writing test cases.

build-aux/bootstrap/rebirth/relibprebirth.scm

@@ -71,9 +71,9 @@
    (define (= x y)
      (string->es "+$$x === +$$y"))
    (define (> x y)
-     (string->es "+$$y > +$$x"))
+     (string->es "+$$x > +$$y"))
    (define (< x y)
-     (string->es "+$$y < +$$x"))
+     (string->es "+$$x < +$$y"))
 
    ;; warning: doesn't verify that it's a pair
    (define (length xs)
@@ -120,7 +120,7 @@
      (string->es "Array.isArray($$xs)"))
    (define (pair? xs)
      (and (list? xs)
-          (> 0 (length xs))))
+          (not (zero? (length xs)))))
 
    ;; R7RS string
    (define (substring s start end)
@@ -129,8 +129,6 @@
      (string->es "$$s.length"))
    (define (string=? s1 s2)
      (string->es "typeof $$s1 === 'string' && $$s1 === $$s2"))
-   (define (string-ref s i)
-     (string->es "$$s[$$i] || $$error(`value out of range: ${$$i}`)"))
    (define (string-append . xs)
      (string->es "$$xs.join('')"))