replace event-stream with through2 (fix processing multiple files)

I get the same [bug1](https://github.com/plus3network/gulp-less/issues/16) and [bug2](https://github.com/plus3network/gulp-less/pull/21) while compiling multiple large coffee files. Replacing stream provider fixed it. 

In glob-stream/index.js is the reason:
```javascript
globber.on('error', stream.emit.bind(stream, 'error'));
globber.on('end', function(){
  stream.end();
});
globber.on('match', function(filename) {
  stream.write({
    cwd: opt.cwd,
    base: basePath,
    path: path.resolve(opt.cwd, filename)
  });
});
```
`stream.end()` may be called before coffee compiles files and passes result to it's callback. Pause/resume in through2 prevent this. 

All tests passed with new stream.
if didn't wrap, then `data = undefined` and test 'should emit errors correctly' failed, ![screen](http://joxi.ru/8bqsU_3JTJBYf4VUyDYg "screen"). BTW if you look on [gulp-stylus](https://github.com/stevelacy/gulp-stylus/blob/master/index.js) there whole plugin wrapped too
```javascript
      if (data.v3SourceMap && file.sourceMap) {
        applySourceMap(file, data.v3SourceMap);
        file.contents = new Buffer(data.js);
      } else {
        file.contents = new Buffer(data);
      }
```