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.
#2532775 - Fixed issue where disabled buttons were still enabled
4 new Button tests and general cleanup
Build button
#2532972 - Added hidden style for button
Button test for show/hide
Build cssbutton
Merge branch 'fix/transition' of https://github.com/prajwalit/yui3 into prajwalit-fix/transition