run `js` as if it were a module at `path`

@param {String} js
@param {String} path
@api private
function run(js, path) {
  var m = new Module(path, module)
  Module._findPath = findPath
  m.paths = Module._nodeModulePaths(dirname(path))
  m.id = path
  m.filename = path
  js = 'module.return=eval(' + json(js) + ')'
  m._compile(js, path)
  Module._findPath = originalFindPath
  return m
}