Respect the prelude's import lists

[gelisam]

Since I'm only importing the Text type, not all of the functions from that module, it should be unambiguous that filter refers to Prelude.filter:

$ cat ~/.hawk/prelude.hs
import Prelude
import Data.Text (Text)

$ hawk 'filter odd [1,2,3]'
error: Won't compile:
    Ambiguous occurrence ‘filter’
It could refer to
    either ‘Prelude.filter’,
        imported from ‘Prelude’ (and originally defined in ‘GHC.List’)
    or ‘Data.Text.filter’, imported from ‘Data.Text’