add implementation for call-completer

scheme/nuit-engine.scm

@@ -777,9 +777,15 @@
      win (result-buffer) (focus-on-result-buffer?))
     (refresh-result-window)))
 
-;; #### implement me
 (define (completer-function-for-command command)
-  #f)
+  (let ((alist
+	 (map (lambda (p)
+		(cons (command-plugin-command p)
+		      (command-plugin-completer p)))
+	      (command-plugin-list))))
+    (cond 
+     ((assoc command alist) => cdr)
+     (else #f))))
 
 (define (call-completer command args prefix arg-pos)
   (cond