Added some additional documentation on JSONP loading, based on Chrome behaviour with mime types

Author: lannymcnie

src/preloadjs/loaders/JSONPLoader.js

@@ -68,9 +68,12 @@ this.createjs = this.createjs || {};
 	 * 			console.log(json.obj.bool); // true
 	 * 		}
 	 *
-	 * Note that JSONP files loaded concurrently require a <em>unique</em> callback. To ensure JSONP files are loaded
-	 * in order, either use the {{#crossLink "LoadQueue/setMaxConnections"}}{{/crossLink}} method (set to 1),
-	 * or set {{#crossLink "LoadItem/maintainOrder:property"}}{{/crossLink}} on items with the same callback.
+	 * JSONP files loaded concurrently require a <em>unique</em> callback. To ensure JSONP files are loaded in order,
+	 * either use the {{#crossLink "LoadQueue/setMaxConnections"}}{{/crossLink}} method (set to 1), or set
+	 * {{#crossLink "LoadItem/maintainOrder:property"}}{{/crossLink}} on items with the same callback.
+	 *
+	 * Important note: Some browsers will prevent JSONP from firing the callback if the file was loaded as JSON, and not
+	 * JavaScript. You may have to have your server give you a JavaScript mime-type for this to work.
 	 *
 	 * @class JSONPLoader
 	 * @param {LoadItem|Object} loadItem

src/preloadjs/loaders/ManifestLoader.js

@@ -61,13 +61,16 @@ this.createjs = this.createjs || {};
 	 * Note that the {{#crossLink "JSONLoader"}}{{/crossLink}} and {{#crossLink "JSONPLoader"}}{{/crossLink}} are
 	 * higher priority loaders, so manifests <strong>must</strong> set the {{#crossLink "LoadItem"}}{{/crossLink}}
 	 * {{#crossLink "LoadItem/type:property"}}{{/crossLink}} property to {{#crossLink "AbstractLoader/MANIFEST:property"}}{{/crossLink}}.
+	 *
+	 * Additionally, some browsers require the server to serve a JavaScript mime-type for JSONP, so it may not work in
+	 * some conditions.
 	 * @class ManifestLoader
 	 * @param {LoadItem|Object} loadItem
 	 * @extends AbstractLoader
 	 * @constructor
 	 */
-	function ManifestLoader(loadItem) {
-		this.AbstractLoader_constructor(loadItem, null, createjs.AbstractLoader.MANIFEST);
+	function ManifestLoader(loadItem, preferXHR) {
+		this.AbstractLoader_constructor(loadItem, preferXHR, createjs.AbstractLoader.MANIFEST);
 
 	// Public Properties
 		/**
@@ -164,7 +167,7 @@ this.createjs = this.createjs || {};
 	 */
 	p._loadManifest = function (json) {
 		if (json && json.manifest) {
-			var queue = this._manifestQueue = new createjs.LoadQueue();
+			var queue = this._manifestQueue = new createjs.LoadQueue(this._preferXHR);
 			queue.on("fileload", this._handleManifestFileLoad, this);
 			queue.on("progress", this._handleManifestProgress, this);
 			queue.on("complete", this._handleManifestComplete, this, true);