The wrong recurring contribution is canceled under certain circumstances

This bug has existed for years - but I finally tracked down the circumstances.

If:

• a contact has multiple recurring contributions tied to the same membership (e.g. renewing a recurring membership at a different rate, or replacing card info that will soon expire);
• The payment processor supports reporting the cancellation;
• You try to cancel the older of the two recurring contributions;

The result is that the NEWER of the two recurring contributions is canceled.

The heart of the reason is in two places:

• CRM_Contribute_Form_CancelSubscription::preProcess calls a function CRM_Contribute_BAO_ContributionRecur::getSubscriptionDetails. It passes through a record ID' and the entity of that record (Contribution, ContributionRecur, Membership).
• getSubscriptionDetails executes a SQL query and returns a single row from the results.

The problem is that a membership can have multiple subscription details, but getSubscriptionDetails only returns one, the newest. So canceling subscription A can lead to subscription B being canceled.

A subsidiary issue is that we throw a fatal error if someone tries canceling a recurring contribution for a membership that's already been canceled. If someone has two recurring contributions, we have to allow them to cancel both, so I'm removing this error check.

Right now, CRM_Contribute_Form_CancelSubscription::preProcess calls getSubscriptionDetails twice if a record has both a crid and mid. I don't understand what code path would allow you to have an mid without a crid - but assuming there is one I'm unaware of, I'm going to submit a PR so that if you have both, we use the crid subscription details, not the mid's.

It's arguable that it shouldn't be allowed to renew an auto-renewing membership, and instead it's treated as an "Update Billing Details" request. However, this disallows renewing at a different rate, so I think this is the best option for now.