(WIP) Get rid of _source

[gaearon]

Should fix #266 and #249.

TODO:

• Fix Webpack loader as well
• Only rely on WeakMap if it's available
• Use global npm package instead of window
• Revive the warning about calling ReactDOM.render() in the same file
• Test edge cases
• Test React Router support (manually)

[nfcampos]

You might want to test this with the kind of tests I have in #269 replacing the call to tag with the set on the global map

[nfcampos]

I think this will update the proxy even if createElement is called with stale type only if we additionally keep a typesById map and do var latestType = typesById.get(id) after this line and use this latestType to update the proxy. Otherwise it doesn't solve the router problem

[gaearon]

The reason stale types were used is because Router cached old types and called createElement with them. Now the only “entry point” to updating a proxy is an explicit __REACT_HOT_LOADER__ call. So router can’t revive old types.

[nfcampos]

Good point.