renaming a function for clarity

lib/fimg-compare.c

@@ -16,7 +16,7 @@ extern int verbosity;		/* must be declared around main() */
 /*
  *	return 0 if images are compatibles
  */
-int fimg_images_compatible(FloatImg *a, FloatImg *b)
+int fimg_images_not_compatible(FloatImg *a, FloatImg *b)
 {
 #if DEBUG_LEVEL > 1
 fprintf(stderr, ">>> %s ( %p %p )\n", __func__, a, b);