Allow overriding jquery's automatic cache-busting on ajax calls

By default jQuery (and Select2) add parameters to ajax calls, to invalidate browser caching. In certain circumstances its useful to disable this (eg when server sets good Cache-Control headers), this patch allows passing the cache/jsonpCallback params though to jquery's ajax function.

select2.js

@@ -346,6 +346,8 @@ the specific language governing permissions and limitations under the Apache Lic
      * @param options.url url for the data
      * @param options.data a function(searchTerm, pageNumber, context) that should return an object containing query string parameters for the above url.
      * @param options.dataType request data type: ajax, jsonp, other datatatypes supported by jQuery's $.ajax function or the transport function if specified
+     * @param options.cache set to true to disable jquery's cache-busting url parameters
+     * @param options.jsonpCallback set to override the jquery callback function - useful in conjunction with options.cache
      * @param options.traditional a boolean flag that should be true if you wish to use the traditional style of param serialization for the ajax request
      * @param options.quietMillis (optional) milliseconds to wait before making the ajaxRequest, helps debounce the ajax function if invoked too often
      * @param options.results a function(remoteData, pageNumber) that converts data returned form the remote request to the format expected by Select2.
@@ -370,6 +372,8 @@ the specific language governing permissions and limitations under the Apache Lic
                     data = options.data, // ajax data function
                     url = ajaxUrl, // ajax url string or function
                     transport = options.transport || $.ajax,
+                    cache = options.cache || false,
+                    jsonpCallback = options.jsonpCallback || undefined,
                     type = options.type || 'GET', // set type of request (GET or POST)
                     params = {};
 
@@ -391,7 +395,8 @@ the specific language governing permissions and limitations under the Apache Lic
                     dataType: options.dataType,
                     data: data,
                     type: type,
-                    cache: false,
+                    cache: cache,
+                    jsonpCallback: jsonpCallback,
                     success: function (data) {
                         if (requestNumber < requestSequence) {
                             return;