support for hoursValid=0

[marcoblancas]

When hoursValid=0 users who has been correctly verified are redirected to de redirectUrl and no download happens.

In our scenario we would like to verify every download because users could have bought just a few submissions.

I think that if admin set hoursValid=0 and the session has been correctly verified user should be allowed to download the galley files they have requested. Later, if user browse another issue and click to download he should be redirected to the redirectUrl in order to be re-verified.

Has it sense?

[asmecher]

Yes, I think that's a sensible use of hoursValid=0.

[marcoblancas]

A pull request with a possible fix is in #9