Discovery of source dependencies without --make

[Lars Hupel]

> I suppose that if --make found Foo.hi, but no Foo.hs, it could simply
> use the Foo.hi.  That would do strictly more than now. I don't know
> if there would be any disadvantages.
> 
> Augmenting --make's semantics sounds better to me than inventing a
> new compilation mode.

Sure, that sounds even better.

> Maybe a feature request ticket.  Then if people like it maybe someone
> can implement it.

Done: <https://ghc.haskell.org/trac/ghc/ticket/9846>

I have no idea how difficult this is going to be – if someone tells me
it's easy, I'll have a stab at it.

Thanks for your help!

Cheers
Lars