darcs patch: add Data.Set.notMember and Data.Map.notMember

[Christian Maeder]

Cale Gibbard wrote:
>> I don't like notElem either
>>
>>> * quite useful for cleaning up guards:
>>>
>>> f x | not (x `Set.member` map) && foo = ...
>>> is hard to read.

I think the plain application "not (Set.member x map) && foo" is more 
appropriate for a programming language like haskell with a somewhat 
limited support of mathematical notations (i.e. not postfix applications).

> Although I'd normally agree with negated versions of things being
> somewhat redundant, the infix version here is rather important, since
> one often wants the code to look the same way as the mathematics. The
> symbols \in and \not\in are both usually written infix, and that's not
> going to change soon. 

latex does not have to consider precedences and the latex sources also 
look much less nice than the final printed version.

Christian