Patch to register XmlSyntax and RegularPatterns as known extensions

[Niklas Broberg]

> I'd like to have concrete XML syntax (HSP) and regular expression
> pattern syntax (HaRP) registered in Language.Haskell.Extension. The
> attached patch registers XmlSyntax and RegularPatterns as constructors
> in the Language.Haskell.Extension.Extension data type, along with
> haddock documentation.

Eh, and to those reading this on the libraries list, the patch was
intended for cabal of course. :-)

Cheers,

/Niklas