Incompatible expression in filter when entering two constants as dot args

```
> filter(data.frame(as.Date("2002-02-02")), TRUE)
  as.Date..2002.02.02..
1            2002-02-02
> filter(data.frame(as.Date("2002-02-02")), TRUE, TRUE)
Error: incompatible expression in filter
```

It isn't a common case, but it occurs in the context of a test suite. Happens also with `filter_`, where it was actually first discovered. Thanks
