The new default setting makes AUC TeX to ask you about
the master file if the file doesn't seem to be a master
(i.e. doesn't contain \docuemtnclass).

July 2001, imz@altlinux.ru

--- auctex-9.9p/tex.el.orig	Wed Jul 25 17:58:12 2001
+++ auctex-9.9p/tex.el	Wed Jul 25 17:58:18 2001
@@ -790,7 +790,7 @@
     (concat (file-name-directory buffer-file-name)
 	    (file-name-directory (TeX-master-file))))))
 
-(defcustom TeX-master t
+(defcustom TeX-master nil
   "*The master file associated with the current buffer.
 If the file being edited is actually included from another file, you
 can tell AUC TeX the name of the master file by setting this variable.