ABSTRACT interfaces + PROCEDURE declarations

[Tobias Schlüter]

Janus Weil wrote:
>> Either would be fine.  Perhaps it is time to carry out the TODO in
>> gfortran.h and make a union of 'cl' and 'derived' .... + 'interface'?
> 
> Ok, so I will go ahead and introduce an interface field into
> gfc_typespec, and while I'm at it also make a union out of cl, derived
> and interface. Fine with everyone?

A minor technicality: since the latter is completely mechanical, I think 
it's best to submit this as a separate patch.  It will also make your 
life easier if this exposes any preexisting latent bugs.

- Tobi