Version 1.6.1

Refined VNode comparison for better exists.

1. Created new property on container: previousVNode. This contains a clone of the previous VNode before patching. This means its element properties all have null values, same as a newly provided VNode would.
2. The patchElement function in vdom.js now check the container's previousVNode property to check with the provided VNode from render. If the two objects are identical, it exists. Before this didn't happen because the default vnode property on the container has references to DOM elements from the last patch.