[CLI] Validation check for "React" package name

[dsibiski]

React (with a capital) should be a reserve word and should not be used as a project name since it will break the Sample app when generated.

Previously, the CLI replaced all occurrences of SampleApp with whatever the user specified. If they happen to input 'React', it would generate this:

var React = React.createClass({ ...

...

AppRegistry.registerComponent('React', () => React);

...which is a redefinition of React, causing createClass to not be defined, in turn causing the app to crash on the very first run after init, without the user modifying anything.

This commit adds a validation check prompting the user that React is not a valid project name.

Discussion here: http://stackoverflow.com/a/30416864/4932710

[ide]

Nice catch. With babel we may also want to use const with all requires so the transformer catches this.

[vjeux]

Nice, more warnings to prevent mistakes :)

@ide: what would fix that is for the packager to yell at you if you have two modules with the same name. Right now, it just picks a random one. Internally we've got a lot of duplicates but hopefully we'll be able to remove them and start warning instead of this very bad behavior.

[ide]

The packager already breaks if there are two @providesModules with the name name (or it used to a couple weeks ago). In this case the index.ios.js file doesn't have a haste header, it's just that there are two variables with the same name.