ctrl-d with readline exits one recursive repl instance

* module/ice-9/buffered-input.scm (make-buffered-input-port): Instead of
  always returning EOF once EOF is seen once, call the producer again.
  Allows Ctrl-D to cause one EOF at the REPL, returning once from a
  recursive edit, but input continues normally. Thanks to Andrew
  Bagdanov for a clue that led to the fix.

THANKS

@@ -21,6 +21,7 @@ Contributors since the last release:
 For fixes or providing information which led to a fix:
 
           David Allouche
+         Andrew Bagdanov
 	 Martin Baulig
         Fabrice Bauzac
         Sylvain Beucler

module/ice-9/buffered-input.scm

@@ -64,7 +64,10 @@ with @var{continuation?} set to @code{#t}."
 	      (lambda ()
 		(cond 
 		 ((eof-object? read-string)
-		  read-string)
+                  (let ((eof read-string))
+                    (set! read-string "")
+                    (set! string-index -1)
+                    eof))
 		 ((>= string-index (string-length read-string))
 		  (set! string-index -1)
                   (get-character))