Change to addComponent

A change to addComponent, as discussed [here](https://groups.google.com/forum/?fromgroups=#!topic/craftyjs/JMPNyq61KlA).

* Only toggles the __c[id] flag when the component is actually added.
* Doesn't add the component if the flag is already true.

The second change might break some code that was relying on the old behavior, but is clearly the better behavior, and without the first change would break things badly.