Use our own md5 library to generate MD5 sum instead of calling an external program.

scheme/lib/pop3.scm

@@ -210,7 +210,9 @@
 (define (pop3-login/APOP connection login password)
   (let* ((key (string-append (pop3-connection-challenge connection)
                              password))
-         (digest (md5-digest key))
+         (digest (number->string
+		  (md5-digest->number (md5-digest-for-string key))
+		  16))
          (status (pop3-send-command connection
                                     (format #f "APOP ~a ~a" login digest))))
   (set-pop3-connection-login! connection login)