Break overly-long lines in type constructor list in import list

Example:

``` Haskell
import Language.Haskell.Syntax (HsExportSpec(HsEVar, HsEAbs, HsEThingAll, HsEThingWith, HsEModuleContents)
```

should be converted to

``` Haskell
import Language.Haskell.Syntax (HsExportSpec(HsEVar, HsEAbs, HsEThingAll,
HsEThingWith, HsEModuleContents)
```

(Note that I'm starting a new line after the last constructor which is still within 80 chars
from the end of the line.)

Start by running stylish-haskell on the import example and locating the formatter entry point for import lists and type constructor lists. Compare the output with the requested 80-character wrapping, then add or update the relevant formatting test so the shown multiline layout is produced.

Written by the indexing model from the issue text.