patch 8.1.0454: resolve() was not tested with a symlink cycle

Problem:    resolve() was not tested with a symlink cycle.
Solution:   Add a test. (Dominique Pelle, closes #3513)
diff --git a/src/testdir/test_functions.vim b/src/testdir/test_functions.vim
index 17f7c19..d601c27 100644
--- a/src/testdir/test_functions.vim
+++ b/src/testdir/test_functions.vim
@@ -190,6 +190,52 @@
   call assert_fails('call strftime("%Y", [])', 'E745:')
 endfunc
 
+func Test_resolve()
+  if !has('unix')
+    return
+  endif
+
+  " Xlink1 -> Xlink2
+  " Xlink2 -> Xlink3
+  silent !ln -s -f Xlink2 Xlink1
+  silent !ln -s -f Xlink3 Xlink2
+  call assert_equal('Xlink3', resolve('Xlink1'))
+  call assert_equal('./Xlink3', resolve('./Xlink1'))
+  call assert_equal('Xlink3/', resolve('Xlink2/'))
+  " FIXME: these tests result in things like "Xlink2/" instead of "Xlink3/"?!
+  "call assert_equal('Xlink3/', resolve('Xlink1/'))
+  "call assert_equal('./Xlink3/', resolve('./Xlink1/'))
+  "call assert_equal(getcwd() . '/Xlink3/', resolve(getcwd() . '/Xlink1/'))
+  call assert_equal(getcwd() . '/Xlink3', resolve(getcwd() . '/Xlink1'))
+
+  " Test resolve() with a symlink cycle.
+  " Xlink1 -> Xlink2
+  " Xlink2 -> Xlink3
+  " Xlink3 -> Xlink1
+  silent !ln -s -f Xlink1 Xlink3
+  call assert_fails('call resolve("Xlink1")',   'E655:')
+  call assert_fails('call resolve("./Xlink1")', 'E655:')
+  call assert_fails('call resolve("Xlink2")',   'E655:')
+  call assert_fails('call resolve("Xlink3")',   'E655:')
+  call delete('Xlink1')
+  call delete('Xlink2')
+  call delete('Xlink3')
+
+  silent !ln -s -f Xdir//Xfile Xlink
+  call assert_equal('Xdir/Xfile', resolve('Xlink'))
+  call delete('Xlink')
+
+  silent !ln -s -f Xlink2/ Xlink1
+  call assert_equal('Xlink2', resolve('Xlink1'))
+  call assert_equal('Xlink2/', resolve('Xlink1/'))
+  call delete('Xlink1')
+
+  silent !ln -s -f ./Xlink2 Xlink1
+  call assert_equal('Xlink2', resolve('Xlink1'))
+  call assert_equal('./Xlink2', resolve('./Xlink1'))
+  call delete('Xlink1')
+endfunc
+
 func Test_simplify()
   call assert_equal('',            simplify(''))
   call assert_equal('/',           simplify('/'))
diff --git a/src/version.c b/src/version.c
index dee74d3..caf7168 100644
--- a/src/version.c
+++ b/src/version.c
@@ -793,6 +793,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    454,
+/**/
     453,
 /**/
     452,