object rest and destructured params

[xjamundx]

We currently support:
var {a, ...b} = c;

But not:
function b({a, ...b}) {}

babylon and babel-eslint support that syntax instead per http://felix-kling.de/esprima_ast_explorer/ though acorn does not.

[xjamundx]

Rough stack trace

TypeError: Cannot read property 'type' of undefined at reinterpretAsDestructuredParameter
 (http://eslint.org/js/app/eslint.js:5674:13) at reinterpretAsDestructuredParameter 
(http://eslint.org/js/app/eslint.js:5681:13) at reinterpretAsCoverFormalsList 
(http://eslint.org/js/app/eslint.js:5512:13) at parseAssignmentExpression 
(http://eslint.org/js/app/eslint.js:5749:22) at parseExpression
(http://eslint.org/js/app/eslint.js:5787:16) at parseExpressionStatement 
(http://eslint.org/js/app/eslint.js:5982:16) at parseStatement 
(http://eslint.org/js/app/eslint.js:6514:44) at parseSourceElement 
(http://eslint.org/js/app/eslint.js:7400:16) at parseSourceElements 
(http://eslint.org/js/app/eslint.js:7433:25) at parseProgram
(http://eslint.org/js/app/eslint.js:7453:12)

[xjamundx]

From the issue200 branch it works beautifully:

> require('./espree').parse('function x({a, ...b}) { }', { ecmaFeatures: { destructuring: true, experimentalObjectRestSpread: true}})
{ type: 'Program',
  body: 
   [ { type: 'FunctionDeclaration',
       id: [Object],
       generator: false,
       expression: false,
       params: [Object],
       body: [Object] } ],
  sourceType: 'script' }

[nzakas]

Working on this.