reformat pretty.rkt a bit

#lang instead of module, spaces instead of tabs, other whitespace and
indentation

racket/collects/racket/pretty.rkt

@@ -9,7 +9,7 @@
 ;; require this module and evaluate:
 ;;      (current-print pretty-print-handler)
 
-(module pretty racket/base
+#lang racket/base
 (require racket/private/port
          racket/flonum
          racket/fixnum)
@@ -1637,5 +1637,5 @@
             (substring s 0 (- (string-length s) 1)))))))
 
 
-  )
+