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/testdir/test_recover.vim b/src/testdir/test_recover.vim
index 33cd54b..2e34985 100644
--- a/src/testdir/test_recover.vim
+++ b/src/testdir/test_recover.vim
@@ -7,7 +7,7 @@
   call assert_fails('recover', 'E305:')
   close!
 
-  if has('win32')
+  if has('win32') || filewritable('/') == 2
     " can write in / directory on MS-Windows
     set dir=/notexist/
   endif
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,