Update 10.4-test-utils.md

This adds minimal valid event data to the Simulate.change example for a text input field.
Update tutorial language to be more explicit.

The word "Friends" does establish a relationship however it does not fit in the vernacular of react. 
This change makes the phrase more explicit and more familiar.
Animation documentation for ReactTransitionGroup

Update to the animation documentation for ReactTransitionGroup to clear the air on where one can use it.

If someone tries to use it off of React.addons.ReactTransitionGroup, which is undefined, instead of its real location, React.addons.TransitionGroup, they get a vague error about being unable to set defaultProps of undefined in the React createElement body.
Remove some invariants and deadcode

These are not necessary if we enable type checks. Static or dynamic.

They're distracting my greppability.

Also, some dead code in shallow rendering.
Merge pull request #2552 from sebmarkbage/cleanupinternals

Remove some unnecessary code in ReactComponents
Merge pull request #2555 from mfunkie/patch-1

Animation documentation for ReactTransitionGroup
Merge pull request #2554 from samccone/patch-1

Update tutorial language to be more explicit.
Merge pull request #2544 from mjul/patch-1

Update 10.4-test-utils.md