Reserved keywords as parameters maybe clobbered

I was looking at some of the strict tests added in 66eb186a74376acded0f637dd504cfc98fc6d44b (by @geraldalewis) and noticed some are generating invalid output. The test only checks if the code can be generated but not evaluated.

There was two different types of errors.

``` coffee
(@case, _case) ->
```

generates

``` js
(function(_case, _case) {
  this["case"] = _case;
});
```

So theres a bug in the variable renaming here.

The second is a little worse.

``` coffee
(@case, _case...) ->
```

generates

``` js
var __slice = [].slice;

(function() {
  var case, _case;
  _case = arguments[0], _case = 2 <= arguments.length ? __slice.call(arguments, 1) : [];
  this["case"] = _case;
});
```

An unused and reversed local is created for `case`.

I haven't looked into a fix yet, but I figured I'd open an patch with tests and maybe someone much more familiar will know what to do.