[GHC] #971: Add intercalate and split to Data.List

[Christian Maeder]

>  = Split =
>  Bulat Ziganshin suggested also adding a function split which is a right
>  inverse of intercalate. Donald Steward seemed to agree with this decision.
>  No one else raised their voice about this so it seems uncontroversial.

I also agree to add a split function. The problem was to agree which
variant should be called split (wrt. to treatment of multiple and final
separators as well as to "Eq" context or predicate argument).

http://article.gmane.org/gmane.comp.lang.haskell.libraries/4862
http://article.gmane.org/gmane.comp.lang.haskell.libraries/4869