patch 7.4.2109
Problem:    Setting 'display' to "lastline" is a drastic change, while
            omitting it results in lots of "@" lines.
Solution:   Add "truncate" to show "@@@" for a truncated line.
diff --git a/src/option.h b/src/option.h
index f05a466..bc8d4e0 100644
--- a/src/option.h
+++ b/src/option.h
@@ -454,10 +454,11 @@
 EXTERN char_u	*p_dy;		/* 'display' */
 EXTERN unsigned	dy_flags;
 #ifdef IN_OPTION_C
-static char *(p_dy_values[]) = {"lastline", "uhex", NULL};
+static char *(p_dy_values[]) = {"lastline", "truncate", "uhex", NULL};
 #endif
 #define DY_LASTLINE		0x001
-#define DY_UHEX			0x002
+#define DY_TRUNCATE		0x002
+#define DY_UHEX			0x004
 EXTERN int	p_ed;		/* 'edcompatible' */
 #ifdef FEAT_WINDOWS
 EXTERN char_u	*p_ead;		/* 'eadirection' */