Update loader.js

Hi, I have not fully tested this but the basic concept seems to work as far as I have tried it.
There is currently a pretty big issue regarding including less and scss files from node packages because most of them are compiled into different directories than where the src file resides. This messes with relative resources. With this minor change people can specify a rel path to trick relative resources to load relative to the supplied path.

example usage:      
```           
    module: {
        loaders: [
            {
                test: /\.less$/,
                loader: ["style-loader", "css-loader", "less-loader"],
                exclude: [
                    /\package\/less\/style.less$/
                ]
            },
            {
                test: /\package\/less\/style.less$/,
                loader: [
                    "style-loader",
                    "css-loader?rel="+path.resolve(__dirname,'path/to/package/dist/css'),
                    "less-loader"
                ]
            }
         ]
     }
```

I just pulled the regx code off of stack overflow. Not sure what the best practice is to detect if a path is relative in javascript.

Author: SplicePHP

lib/loader.js

@@ -14,6 +14,7 @@ module.exports = function(content, map) {
 	var callback = this.async();
 	var query = loaderUtils.parseQuery(this.query);
 	var root = query.root;
+	var rel = query.rel;
 	var moduleMode = query.modules || query.module;
 	var camelCaseKeys = query.camelCase || query.camelcase;
 
@@ -81,6 +82,9 @@ module.exports = function(content, map) {
 							url.substr(idx);
 				}
 				urlRequest = url;
+				if(!(/^(?:\/|[a-z0-9]+:\/\/)/.test(urlRequest)) && typeof rel !== 'undefined' ) {
+                                    urlRequest = rel + "/" + urlRequest;
+                                }
 				return "\" + require(" + loaderUtils.stringifyRequest(this, urlRequest) + ") + \"";
 			}.bind(this));
 		}