fluent/fluentd — pull request #510 by sonots (2014-12-14 12:21:03+00:00)
Title: add router.emit and router= for compatibility with v0.12

To support the label feature implemented in v0.12, input/output plugins must be modified as:

```diff
- Engine.emit
+ router.emit
```

Also, kinds of MultiOutput plugin such as config-expander must be modified like:

```diff
output = Plugin.new_output(type)
+ output.router = router
output.configure(e)
```

This patch makes the above modification works in both v0.12 and v0.10 branch.