Set textarea value when changing content

At http://jsfiddle.net/spicyj/W4QLq/, typing into the textbox would cause
clicking the button to do nothing; now it should work.
Don't set value if it'll be a noop
Don't let textarea value change via textContent

Turns out my tests before weren't particularly useful because
receiveProps doesn't end up running componentDidUpdate since the
transaction never finishes. Now they use replaceProps instead (and I
verified that commenting out the "rootNode.value = ..." line makes the
tests fail, which wasn't true before).
Merge remote-tracking branch 'origin/master' into textarea-update-value
Don't update value or textContent unnecessarily

_updateDOMChildren was already updating textContent so we don't need to
do it in _updateDOMProperties. Additionally, don't update .value if
it'll be a noop because it has side-effects (like moving the cursor) in
some browsers (like IE 9).

Refactor tests to be a bit more robust and a bit cleaner too.
Remove textContent tests; they break in phantomjs
Merge branch 'textarea-update-value' of git://github.com/spicyj/react

Conflicts:
	src/core/ReactDefaultInjection.js