CRM-14573: ts fixes for 4.4

CRM/Event/Cart/Form/Checkout/Payment.php, templates.../CRM/Contribute/Form/ContributionPage/Tab.hlp

I would prefer to have this committed to 4.4, since these strings are pretty broken and they have been causing problems to translators using an external editort. When gettext compiles the .po files, it fails because the number of tailing newlines does not match.