Merge pull request #5467

6171e49 [Qt] Use identical strings for expired payment request message (Philip Kaufmann)
06087bd [Qt] minor comment updates in PaymentServer (Philip Kaufmann)
35d1595 [Qt] constify first parameter of processPaymentRequest() (Philip Kaufmann)
9b14aef [Qt] take care of a missing typecast in PaymentRequestPlus::getMerchant() (Philip Kaufmann)
d19ae3c [Qt] remove unused PaymentRequestPlus::getPKIType function (Philip Kaufmann)
6e17a74 [Qt] paymentserver: better logging of invalid certs (Philip Kaufmann)
5a53d7c [Qt] paymentserver: do not log NULL certificates (Philip Kaufmann)