patch 8.0.0294: argument list is not stored correctly in a session file

Problem:    Argument list is not stored correctly in a session file.
            (lgpasquale)
Solution:   Use "$argadd" instead of "argadd". (closes #1434)
diff --git a/src/testdir/test_mksession.vim b/src/testdir/test_mksession.vim
index a51180c..6ea3255 100644
--- a/src/testdir/test_mksession.vim
+++ b/src/testdir/test_mksession.vim
@@ -110,4 +110,16 @@
   call delete('Xtest_mks.out')
 endfunc
 
+func Test_mksession_arglist()
+  argdel *
+  next file1 file2 file3 file4
+  mksession! Xtest_mks.out
+  source Xtest_mks.out
+  call assert_equal(['file1', 'file2', 'file3', 'file4'], argv())
+
+  call delete('Xtest_mks.out')
+  argdel *
+endfunc
+
+
 " vim: shiftwidth=2 sts=2 expandtab