patch 9.0.0067: cannot show virtual text

Problem:    Cannot show virtual text.
Solution:   Initial changes for virtual text support, using text properties.
diff --git a/src/errors.h b/src/errors.h
index 965187f..e8008fd 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -3310,3 +3310,7 @@
 EXTERN char e_cmdline_window_already_open[]
 	INIT(= N_("E1292: Command-line window is already open"));
 #endif
+#ifdef FEAT_PROP_POPUP
+EXTERN char e_cannot_use_negative_id_after_adding_textprop_with_text[]
+	INIT(= N_("E1291: Cannot use a negative id after adding a textprop with text"));
+#endif