patch 9.0.0781: workaround to rename "small" to "smallfont" is clumsy

Problem:    Workaround to rename "small" to "smallfont" is clumsy.
Solution:   Undefine "small" after including windows.h. (Ken Takata)
diff --git a/src/version.c b/src/version.c
index 947f653..8d690ca 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    781,
+/**/
     780,
 /**/
     779,