64-bit integer conversion support

[Arseny Kapoulkine]

Hello, Decio.

> If performance is not critical, why not do an mpz_get_ui(), a shift
> by 32, then another mpz_get_ui(), and concatenate these two?

Hmm, that's potentially O(N), but if N is >2, then the caller did not
want to use converting to 64 bit anyway...

That's a way to go, thanks for the idea. If there are better
approaches though, I'm still interested in them :)

-- 
Best regards,
 Arseny                          mailto:arseny.kapoulkine at gmail.com