Add a JNDIResourceLoader

I'm trying to integrate LESS with JAWR 3.3 (using a modified version of eliotsykes/less-css-jawr). JAWR configuration uses servlet-relative paths, which are then passed to ServletContext.getResource() to get a jndi:// URL, which I pass to engine.compile(). When LessEngine gets the jndi URL, no ResourceLoader handles it.

I have a working patch that is just a copy/paste of HTTPResourceLoader with a different schema.