Refine the regexp for checking the options against '-c' option
to diff; make it *not* match smth like 
"--ignore-space-change --ignore-blank-lines".

imz@altlinux.ru, Nov 2002.

--- 21.2/lisp/ediff-diff.el.check-c	2002-11-17 23:46:05 +0300
+++ 21.2/lisp/ediff-diff.el	2002-11-17 23:58:26 +0300
@@ -223,7 +223,7 @@
 ;; ediff-setup-diff-regions-function, which can also have the value
 ;; ediff-setup-diff-regions3, which takes 4 arguments.
 (defun ediff-setup-diff-regions (file-A file-B file-C)
-  (if (string-match "c" ediff-diff-options)
+  (if (string-match "\\(^\\|[[:space:]]\\)-[^-]*c" ediff-diff-options)
       (error "Option `-c' is not allowed in `ediff-diff-options'"))
 						  
   ;; create, if it doesn't exist