Fix bug in IE10 with MutationObserver

There is a difference in behavior between MutationObserver and this shim
in IE10, causing the target for a MutationRecord to be different from
the expect value.

This happens because when you append a node with children in IE10 it'll call the
DOMNodeInserted for the node and its children seperately.

The test has an if statement because the behavior is different between
IE10 and chrome, making both outcomes valid.

To test this PR you'll have to open the runner in IE10