Add some autoconf warnings

[Anssi Hannula]

Chris Morgan wrote:
> Given the huge amount of output from configure I think it would make
> sense to print out what was and wasn't supported as far as modules. 
> The handful of extra lines would save people from being confused about
> whether support was or wasn't built in.  Other projects print this
> data out at the end of a configure run and I've found it quite useful.

I agree. It would be a nice feature.

-- 
Anssi Hannula