Request: withArrayLength

[Simon Marlow]

> The suggestion wasn't to rename it, but to move it from base 
> to haskell98.
> 
> Then you could add these functions without changing the 
> interface of any
> of the modules listed in the FFI Addendum.

That would amount to saying that 'Foreign' isn't a hierarchical library
any more, and anyone wishing to use purely hirerarchical libraries in
their code should avoid it.

On one hand, this looks reasonable: Foreign already doesn't re-export
Foreign.C.  However, I do use it all the time.  So if we ever decided to
allow disabling of the haskell98 package, lots of supposedly
purely-hierarchical code would break.  Ho hum.

Cheers,
	Simon