prevent "double" transforms (caused by watchify)

when using watchify, required templates get compiled as needed up the require stream. 

in the wild: 

``` 
// file: app.js
module.exports = function({
  require('template.ejs)
})
```

using watchify, a change to `template.ejs` would trigger a transform of `template.ejs`, and then of `app.js`. at that point everything gets messed up.