Keep arguments across statement wrappers

[satyr]

So that this:
$ coco -e 'console.log arguments is (switch case 1 then arguments)'
false
results in true.

Before

console.log(arguments === (function(){
  switch (false) {
  case !1:
    return arguments;
  }
}.apply(this, arguments)));

After

console.log(arguments === (function(_args){
  switch (false) {
  case !1:
    return _args;
  }
}(arguments)));

[satyr]

closed by 7dd7f98; statement wrappers now precisely emulate arguments