Fix test cases.

First, regions have a pointer to its el. No need for a lookup.
Second, I'm detaching all contents before running the replaces.
Third, never replace top view's el, just modify.
Use cloning. Sorry, screwed that up.
Add Test 4.

It uses a placeholder, so we don't have to detach each child node, just
the parent.
Merge pull request #1 from jridgewell/master

Fix test cases.