patch 8.0.1378: autoload script sources itself when defining function

Problem:    Autoload script sources itself when defining function.
Solution:   Pass TFN_NO_AUTOLOAD to trans_function_name(). (Yasuhiro
            Matsumoto, closes #2423)
diff --git a/src/testdir/test_autoload.vim b/src/testdir/test_autoload.vim
index a92851f..7396c22 100644
--- a/src/testdir/test_autoload.vim
+++ b/src/testdir/test_autoload.vim
@@ -2,10 +2,16 @@
 
 set runtimepath=./sautest
 
-func! Test_autoload_dict_func()
+func Test_autoload_dict_func()
   let g:loaded_foo_vim = 0
   let g:called_foo_bar_echo = 0
   call g:foo#bar.echo()
   call assert_equal(1, g:loaded_foo_vim)
   call assert_equal(1, g:called_foo_bar_echo)
 endfunc
+
+func Test_source_autoload()
+  let g:loaded_sourced_vim = 0
+  source sautest/autoload/sourced.vim
+  call assert_equal(1, g:loaded_sourced_vim)
+endfunc