rename file

renamed file is empty

```
test('rename file', function(fs, t) {
var contents = 'foo';
fs.writeFile('/foo', contents, function() {
fs.rename('/foo', '/bar', function(err) {
fs.readFile('/bar', function(err, buf) {
t.notOk(err);
t.same(buf.toString(), contents); // buf.toString() === ''
t.end();
});
});
});
});
```

Start with the inline “rename file” test and trace the fs.rename and fs.readFile entry points it exercises. Reproduce the failure, then verify that renaming /foo to /bar preserves the original contents and that the test passes.

Written by the indexing model from the issue text.