improve reucrsive watch

This commit improve recursive option of --watch.
With -m or --matchdir option it works to watch files recursively,
and it compiles files which has changed into the same directory structure in --output dir.
Well, it will still present the same problem.

Lest try:

```javascript
var out = path.basename(options.src);

if (options.m && options.inputDir) {
  out = path.relative(options.inputDir, options.src);
}
```