Improve test for operating system in org-ctags.el

lisp/ChangeLog

@@ -1,5 +1,7 @@
 2010-01-15  Carsten Dominik  <carsten.dominik@gmail.com>
 
+	* org-ctags.el (org-ctags-path-to-ctags): Better system-type test.
+
 	* org-latex.el (org-export-latex-treat-backslash-char): Do not by
 	accident protect a character that is before a backslash.
 

lisp/org-ctags.el

@@ -132,14 +132,14 @@ Format is: /REGEXP/TAGNAME/FLAGS,TAGTYPE/
 See the ctags documentation for more information.")
 
 (defcustom org-ctags-path-to-ctags 
-  (case (operating-system)
-    (windows "ctags.exe")
-    (unix "ctags-exuberant"))
+  (case system-type
+    (windows-nt "ctags.exe")
+    (darwin "ctags-exuberant")
+    (t "ctags-exuberant"))
   "Full path to the ctags executable file."
   :group 'org-ctags
   :type 'file)
 
-
 (defcustom org-ctags-open-link-functions
   '(org-ctags-find-tag 
     org-ctags-ask-rebuild-tags-file-then-find-tag