Node require completion

This PR gives the capability to have completion on require node module (locals like fs and custom modules)
It uses hook completion feature https://github.com/marijnh/tern/commit/180f146ab835e744072c89a8ef99e90af8d3a840 inside the node.js tern plugin.

Here a screenshot with eclipse : 

![eclipseternnoderequirecompletion](https://cloud.githubusercontent.com/assets/1932211/5232651/e0ad7ae8-7756-11e4-99b4-ef4c8d2cbf37.png)

Here some information : 
 * I had copied/paste several function from tern.js like resolvePos
see https://github.com/angelozerr/tern/blob/node-require-compeltion/plugin/node.js#L282
It should be cool if those functions could be public inside tern.
 * there is 2 new tests with require modules
 * the compeltion result returns isStringAround, startQuote, endQuote too.

@marijnh  Hope you will like and accept this patch. Don't hesitate to tell me if you wish I change something.