Do not merge attributes that are the same

The logic for merging attributes will essentially concatenate values if an attribute is in the DOM element and is in the partial that will be replacing the DOM element.  This doesn't make sense in some use cases, but the most clear one is where there is something like an ID which is the exact same in both. The current logic will concatenate `<div id="myid" my-directive>` and `<div id="myid">` (for the directive template) into `<div id="myid myid">`.

This pull request is to add one very simple condition that will just ensure that when the values are exactly the same, they are not concatenated.