Get ready for AMP and fix a deprecated import

As you might be well aware, the Applicative-Monad Proposal is on its second stage, and GHC 7.8 issues a warning if a Monad isn't also an Applicative. Such instances will break in GHC 7.10. So I added those instances where needed, and fixed one deprecated import as well.

A problem that remains is a future name clash:
```
src/Data/DLists.hs:61:1: Warning:
    Local definition of ‘join’ clashes with a future Prelude name - this will become an error in GHC 7.10, under the Applicative-Monad Proposal.
```

We can either rename `join` to `append` (as in the `dlist` package), or even switch to using `dlist`.