Tests: Improve jsonp tests

Since global variable for callback always would be equal to undefined value
it better to check for boolean instead

test/data/testrunner.js

@@ -196,7 +196,7 @@ window.Globals = (function() {
 	return {
 		register: function( name ) {
 			globals[ name ] = true;
-			supportjQuery.globalEval( "var " + name + " = undefined;" );
+			supportjQuery.globalEval( "var " + name + " = true;" );
 		},
 		cleanup: function() {
 			var name,

test/unit/ajax.js

@@ -728,7 +728,7 @@ module( "ajax", {
 				jsonpCallback: "functionToCleanUp",
 				success: function( data ) {
 					ok( data["data"], "JSON results returned (GET, custom callback name to be cleaned up)" );
-					strictEqual( window["functionToCleanUp"], undefined, "Callback was removed (GET, custom callback name to be cleaned up)" );
+					strictEqual( window["functionToCleanUp"], true, "Callback was removed (GET, custom callback name to be cleaned up)" );
 					var xhr;
 					jQuery.ajax({
 						url: "data/jsonp.php",
@@ -742,7 +742,7 @@ module( "ajax", {
 					});
 					xhr.fail(function() {
 						ok( true, "Ajax error JSON (GET, custom callback name to be cleaned up)" );
-						strictEqual( window["functionToCleanUp"], undefined, "Callback was removed after early abort (GET, custom callback name to be cleaned up)" );
+						strictEqual( window["functionToCleanUp"], true, "Callback was removed after early abort (GET, custom callback name to be cleaned up)" );
 					});
 				}
 			}, {