Enable running single test

[Garry Yao]

In unit testing, previously we've been used the following trick a lot to force executing only one specific test:

// Run one specific test without registering to YUI runner.
window.onload = testCase.testName;

Now when adapting to our new testing system CKTester( #4218 ), the old approach doesn't work at all, so this ticket is intended to figure out a better way for achieving the same goal without change CKTester.

One official way ( from YUI Test functionality ) is to use the following declaration on a test case:

var oTestCase = new YAHOO.tool.TestCase({
	_should: {
		ignore: {
			testName: true //ignore this test
		}
	}
});

But this is inconvenient when we want to ignore all tests but one, so I'm suggesting of extending YUI Test to support a more simpler syntax:

	_should: {
		ignoreAllBut: {
			testName: true //ignore all tests except this, comment this line to toggle it.
		}
	}

Test case written in this manner should be more easier to understand and modify.