patch 8.0.0600: test_recover fails on some systems

Problem:    test_recover fails on some systems.
Solution:   Explicitly check if "/" is writable. (Ken Takata)
diff --git a/src/version.c b/src/version.c
index a572ae3..7262a3d 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    600,
+/**/
     599,
 /**/
     598,