patch 8.1.0579: cannot attach properties to text

Problem:    Cannot attach properties to text.
Solution:   First part of adding text properties.
diff --git a/src/Make_all.mak b/src/Make_all.mak
index 466f17e..4aa30b8 100644
--- a/src/Make_all.mak
+++ b/src/Make_all.mak
@@ -186,6 +186,7 @@
 	test_terminal_fail \
 	test_textformat \
 	test_textobjects \
+	test_textprop \
 	test_timers \
 	test_true_false \
 	test_undo \