patch 9.0.0144: text property cannot override 'cursorline' highlight

Problem:    Text property cannot override 'cursorline' highlight.
Solution:   Add the "override" flag to prop_type_add(). (closes #5533,
            closes #8225).
diff --git a/runtime/doc/textprop.txt b/runtime/doc/textprop.txt
index 150d466..fd91333 100644
--- a/runtime/doc/textprop.txt
+++ b/runtime/doc/textprop.txt
@@ -377,6 +377,8 @@
 		   combine	when omitted or TRUE combine the highlight
 				with any syntax highlight; when FALSE syntax
 				highlight will not be used
+		   override	when TRUE the highlight overrides any other,
+				including 'cursorline' and Visual
 		   start_incl	when TRUE inserts at the start position will
 				be included in the text property
 		   end_incl	when TRUE inserts at the end position will be