AbstractRequest = function (item) {
		this._item = item;
	}
A base class for actual data requests, such as {{#crossLink "XHRRequest"}}{{/crossLink}}, {{#crossLink "TagRequest"}}{{/crossLink}},
and {{#crossLink "MediaRequest"}}{{/crossLink}}. PreloadJS loaders will typically use a data loader under the
hood to get data.
@class AbstractRequest
@param {LoadItem} item
@constructor