patch applied (ghc): Type checking for type synonym families

[Manuel M T Chakravarty]

>   * Type checking for type synonym families
>   
>   This patch introduces type checking for type families of which associated
>   type synonyms are a special case.

Please note that this is very experimental code.  We have tried hard 
to ensure that it does not break existing code (scream if it still 
does!) and all the basic machinery for type families is in place. 
However, there are still significant known bugs and shortcomings in 
the type family support.  Nevertheless, if you are the bleeding edge 
kind of person, give it a whirl and file those bug reports ;)

Please note that type families will not be an officially announced 
and supported feature in 6.8.  So, until the 6.8 branch, the 
priority is to shake out any bugs that break existing code, not to 
polish type families.

Manuel