Payment Method field (payment_processor) should not be required if total fee is $0

This is a regression (although it's been broken since 4.1). When we added support for multiple payment processor options + pay later as a radio button, this bug was introduced.

The form rule for payment_processor should check if total fee and not require a selection if it's 0.

Screenshot attached.

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I searched Jira for issues mention this, but found no issues besides this very old one: http://issues.civicrm.org/jira/browse/CRM-2534

Basically if you have an event fee with a zero option, along with other paid options, the payment select as well as credit card fields show up still. The payment option is required. The credit card can be left blank, but is still confusing to the registrant.

This was NOT true in 3.4 according to a recent upgrade which used with a 100% discount through the CiviDiscount module. In 4.3 it appears to be true whether CiviDiscount is used or not, even without the module a zero option requires payment choice.