failsafe if "which" is not executable.

scheme/httpd/surflets/web-server/root/surflets/admin-profiling.scm

@@ -11,6 +11,7 @@
 	let-opt
 	receiving
 	primitives
+	handle-fatal-error
 	)
   (begin
 
@@ -310,10 +311,13 @@ plot '~a' title 'SUrflet Profiling ~a' with lines"
       (profile req))
 
     (define (search-executable exec-name)
+      (with-fatal-error-handler
+       ;; If `which' is unavailable, return nothing.
+       (lambda (condition decline) "")
        (receive (status ports) (run/collecting (1) (which ,exec-name))
 	 (if (zero? status)
 	     (read-line ports)
-	    "")))
+	     ""))))
     
     (define (emph text)
       `(font (@ (color "red")) ,text))
@@ -327,5 +331,4 @@ plot '~a' title 'SUrflet Profiling ~a' with lines"
 	     `(tr (td (@ (colspan 2))
 		      ,(emph "Note: There is no executable."))))))
 
-;; TODO: check `where' tool 
     ))