patch 9.0.0411: only created files can be cleaned up with one call

Problem:    Only created files can be cleaned up with one call.
Solution:   Add flags to mkdir() to delete with a deferred function.
            Expand the writefile() name to a full path to handle changing
            directory.
diff --git a/src/testdir/test_eval_stuff.vim b/src/testdir/test_eval_stuff.vim
index 3669cfd..0081d89 100644
--- a/src/testdir/test_eval_stuff.vim
+++ b/src/testdir/test_eval_stuff.vim
Binary files differ