Fix update macros for gnutls and physfs

Fix "downdates" reported by Niels Kristian Bech Jensen for packages
gnutls and physfs by sorting version numbers properly and allowing
(in the case of gnutls) version number parts with more than one digit.
Update package libgomp

Set version number of libgomp to 4.8.0, as its source is contained in
the gcc sources anyway.