Custom writer for function objects

When printing function objects, display its lambda-list.

This could be done via PRINT-OBJECT in theory, but PRINT-OBJECT is not
being dispatch from WRITE function. See issue jscl-project#444

Example of how functions are printed after this commit:

```
  CL-USER> #'prin1-to-string
  #<FUNCTION PRIN1-TO-STRING (FORM)>
  CL-USER> #'prin1
   <FUNCTION PRIN1 (FORM &OPTIONAL STREAM)>
```

src/print.lisp

@@ -331,6 +331,18 @@
            " :count ~d>")
    (hash-table-count form)))
 
+;; function object printer
+(defun function-object-printer (form stream)
+  (let ((res))
+    (setq res (concat "#<FUNCTION "
+		      (or (jscl::oget form "fname")
+			  "")
+		      " "
+		      (or (and (jscl::function-lambda-list form)
+			       (princ-to-string (jscl::function-lambda-list form))) "")
+		      ">"))
+    (simple-format stream res)))
+
 #+jscl
 (defun write (form &key (stream *standard-output*))
   (cond ((mop-object-p form)
@@ -339,7 +351,9 @@
          (invoke-object-printer #'hash-table-object-printer form stream))
         ((structure-p form)
          (invoke-object-printer #'structure-object-printer form stream))
-        (t  (let ((stream (output-stream-designator stream)))
+	((functionp form)
+         (invoke-object-printer #'function-object-printer form stream))
+	(t  (let ((stream (output-stream-designator stream)))
               (multiple-value-bind (objs ids)
                   (scan-multiple-referenced-objects form)
                 (write-aux form stream objs ids)