If module compilation fails, then do not record updates for HMR

Fixes https://github.com/webpack/webpack-dev-server/issues/42, makes #418 unneeded.

Works fine with style-loader, react-hot-loader as-is. 

Allows module compilation errors to occur without disrupting hot module reloading. When a previously failed module compilation succeeds, hot module reloading continues working as normal, without any special code needed in the HMR handlers.