patch 8.1.1960: fold code is spread out

Problem:    Fold code is spread out.
Solution:   Move fold functions to fold.c.
diff --git a/src/version.c b/src/version.c
index 485af13..4435314 100644
--- a/src/version.c
+++ b/src/version.c
@@ -762,6 +762,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1960,
+/**/
     1959,
 /**/
     1958,