Proposal: add exeExtension to System.Info

[Neil Mitchell]

Hi Bulat,

> > I am proposing to add the following to the System.Info module (which
> > seems to be the best place to collect OS-specific things) - the code
>
> why not to add them to FilePath library instead?

Dimitry asked me about this, I said that its probably not the right
place. Which extensions should be used are not related to the way of
handling filepath's, they are a System specific piece of information.

It's best to put stuff where they belong, rather than avoid base like
the plague because its hard to upgrade. The solution to that problem
is modifying base or GHC appropriately.

Thanks

Neil