better messages on failed autocompilation

* libguile/load.c (auto_compile_catch_handler):
* module/ice-9/boot-9.scm (load-in-vicinity): Nicer messages when
  autocompilation fails.

module/ice-9/boot-9.scm

@@ -3506,8 +3506,14 @@ module '(ice-9 q) '(make-q q-length))}."
                  (else #f))))))
       (lambda (k . args)
         (format (current-error-port)
-                ";;; WARNING: compilation of ~a failed:\n;;; key ~a, throw_args ~s\n"
-                name k args)
+                ";;; WARNING: compilation of ~a failed:\n" name)
+        (for-each (lambda (s)
+                    (if (not (string-null? s))
+                        (format (current-error-port) ";;; ~a\n" s)))
+                  (string-split
+                   (call-with-output-string
+                    (lambda (port) (print-exception port #f k args)))
+                   #\newline))
         #f)))
 
   (define (absolute-path? path)