Support JavaScript Templating with EJS

My rails project use JST using EJS.
Because Sprockets supports jst of EJS. 
I want to raplace the rails project with Node.js.
So,I want to support JST using ejs.

This patch modifies below

if asset path includes "jst.ejs" ,  ejs engine returns the string parseing  and envolving
function otherwise the same as before.