Client ready guarantee broken when setting property in manually handled notification event

[sorvell]

If the following is done:

1. a host element manually listens for a notifying event (e.g. on-foo-changed="handleFoo")
2. a client fires the event when it initially flushes properties
3. the host sets a property that triggers a flush in the event handler

A number of bad things happen:

1. the host element can call readyClients twice
2. this can lead to the shadowRoot being appended to itself which triggers Appending a shadowRoot to itself should produce consistent result webcomponents/shadydom#149
3. the ordering guarantee that clients should be ready before host side effects are processed is broken.

This example shows #2 above: http://jsbin.com/wepamiv/edit?html,output (Note that the output should show After hi but does not.