patch 8.1.2019: 'cursorline' always highlights the whole line

Problem:    'cursorline' always highlights the whole line.
Solution:   Add 'cursorlineopt' to specify what is highlighted.
            (closes #4693)
diff --git a/src/structs.h b/src/structs.h
index 0e61f87..ab94a32 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -249,6 +249,8 @@
 # define w_p_cuc w_onebuf_opt.wo_cuc	// 'cursorcolumn'
     int		wo_cul;
 # define w_p_cul w_onebuf_opt.wo_cul	// 'cursorline'
+    char_u	*wo_culopt;
+# define w_p_culopt w_onebuf_opt.wo_culopt	// 'cursorlineopt'
     char_u	*wo_cc;
 # define w_p_cc w_onebuf_opt.wo_cc	// 'colorcolumn'
 #endif