Fix: Improve monkeypatching for ESLint v2.3.0

[mysticatea]

Since v2.3.0, ESLint came to use keys and childVisitorKeys options instead of extending estraverse. VisitorKeys.
ESLint team has the plan to add the ability which extends VisitorKeys into parser plugins, but it may take a long time.

So this PR improves monkey patching for those options.

[hzoo]

Thanks @mysticatea!

I added in

babel-eslint/index.js

Line 353 in 32848e5

exports.VisitorKeys = t.VISITOR_KEYS;

- is that not necessary anymore?

Also for this PR, I would bump https://github.com/babel/babel-eslint/blob/master/package.json#L36 to 2.3.0 so it will actually run on it.

[mysticatea]

Ouch, I updated https://github.com/babel/babel-eslint/blob/master/package.json#L36 to 2.3.0, then 1 test came to failing.
I'm investigating it.

[hzoo]

Ah ok, it might not be due to your change specifically though

[mysticatea]

Anyway, I share it.

[mysticatea]

I'm sorry, I don't have enough time to investigate it today (JST)...

[hzoo]

Thanks - maybe I can check it out tonight

 1) verify fixes issues with flow types and ObjectPattern:
     Error: Expected 0 message(s), got 4 [{"ruleId":"no-unused-vars","severity":1,"message":"'Foo' is defined but never used","line":3,"column":16,"nodeType":"Identifier","source":"  foo({ bar }: Foo) { bar; }"},{"ruleId":"no-shadow","severity":1,"message":"'Foo' is already declared in the upper scope.","line":3,"column":16,"nodeType":"Identifier","source":"  foo({ bar }: Foo) { bar; }"},{"ruleId":"no-unused-vars","severity":1,"message":"'Foo' is defined but never used","line":4,"column":16,"nodeType":"Identifier","source":"  bar({ foo }: Foo) { foo; }"},{"ruleId":"no-shadow","severity":1,"message":"'Foo' is already declared in the upper scope.","line":4,"column":16,"nodeType":"Identifier","source":"  bar({ foo }: Foo) { foo; }"}]
      at verifyAndAssertMessages (test/non-regression.js:28:11)
      at Context.<anonymous> (test/non-regression.js:1353:5)

Looks like it's scoping issue with flow types - we can still merge since it we have the if checks and shouldn't cause more issues

[hzoo]

Reran the tests-

[mysticatea]

@nzakas is faster than me.

• That test failing is caused by here. This patching is changing traversing properties dynamically. But it cannot be changed dynamically in my way.
• babel-eslint seems to work with eslint@2.4.0.

So I just remove throwing an error when estraverse-fb has not found.