Fix show, hide and toggleView methods in transition module

Deals with - http://yuilibrary.com/forum/viewtopic.php?p=36173
Checking for type instead of assigning empty callback.
Merge branch 'fix/transition' of https://github.com/prajwalit/yui3 into prajwalit-fix/transition
Apply toggleView() with arguments to handle overloading.
Move to tests/unit.
Move to tests/unit.
Avoid rewriting tab panel content.
Merge pull request #1 from msweeney/prajwalit-fix/transition

Prajwalit fix/transition
Allow 'label' to accept a Y.Node instance (brings inline with 'content')
Add tests for Y.Node instance label/content and event clobbering.
Add label/content getter tests.
Allow label to be handled via the getter rather than parsing from html.
Include HTML when testing label value from existing markup.
Merge branch 'fix/transition' of https://github.com/prajwalit/yui3 into prajwalit-fix/transition
Merge branch 'prajwalit-fix/transition' into dev-master
Merge branch 'dev-master' into tab-events
Merge branch 'tab-events' into dev-master
Build transition.
Build tabview.
Correct typos in Event and Node docs