Allow (some) method names that happen to be keywords

This should work:

``` powershell
class MyClass {     
    [object] Filter() {
        return $null
    }
}
```

Copied from TFS task 1358992

Reminder to close this Connect bug if this work gets done: https://connect.microsoft.com/PowerShell/Feedback/Details/1709557
