We don't build in 2.10.3

I noticed today that Lift WebKit's LiftScreen doesn't build in 2.10.3, as discussed [here](https://groups.google.com/d/msg/liftweb/5ka_RzZrQSo/PBBr0QqPV08J). It appears to be a type issue associated with how the latest 2.10's handle parameterized types. Specifically, in this code, 2.10.0 used to allow for the following:

```scala
stuff.collect {
  case AFilter(f) => f
}.toList
```

Where `f` is of type `T=>T`. This would result in a `List[T=>T]` so you could feed it into areas requiring a `List[T=>T]`. Except, the newer 2.10's seem to think that this code can generate a "list of something to something where some of those somethings are descendants of T" (best English rendering of the error message).

The fix appears to be to replace these with

```scala
stuff.collect {
  case filter: AFilter[T] => filter.f
}
```

Fix is in progress.