Allow rendering markup string without checksum and React ID

This fixes https://github.com/facebook/react/pull/994.
Also fixes https://github.com/facebook/react/issues/1079.
Server-rendering without ID/checksum now works. Also won't call didMount.
simplify `mountImageIntoNode`'s way of putting markup in innerHTML

Instead of removing the node from the document before changing its innerHTML, just do it directly.
The comment seems to be outdated for years. http://jsperf.com/detach-while-setting-innerhtml
Fix transaction test comments

Probably got copy/pasted in.
update docblock

...for typechecking.
Break more browser deps in core

This is part of what Sebastian suggested. We require it into every component that explicitly needs it and inject it as a default mixin for composite components in
the browser environment. This change frees us up to inject everything in ReactComponent.