patch 8.2.0427: it is not possible to check for a typo in a feature name

Problem:    It is not possible to check for a typo in a feature name.
Solution:   Add an extra argument to has().
diff --git a/src/testdir/test_functions.vim b/src/testdir/test_functions.vim
index f904cc0..96d7f31 100644
--- a/src/testdir/test_functions.vim
+++ b/src/testdir/test_functions.vim
@@ -20,6 +20,14 @@
   call assert_equal(0, bufexists('Xfoo'))
 endfunc
 
+func Test_has()
+  call assert_equal(1, has('eval'))
+  call assert_equal(1, has('eval', 1))
+
+  call assert_equal(0, has('nonexistent'))
+  call assert_equal(0, has('nonexistent', 1))
+endfunc
+
 func Test_empty()
   call assert_equal(1, empty(''))
   call assert_equal(0, empty('a'))
@@ -1586,7 +1594,7 @@
   call assert_equal(2, a)
 
   " confirm() should return 0 when pressing CTRL-C.
-  call feedkeys("\<C-c>", 'L')
+  call feedkeys("\<C-C>", 'L')
   let a = confirm('Are you sure?', "&Yes\n&No")
   call assert_equal(0, a)