Turn new diag message into a link.

Turn new diag message into a link.

This turned out to be a bit of work. When running the porting tests,
the pod checker checks whether all links are valid. To do so, it
creates a database of all valid targets, and then for all links,
checks whether the target exist. However, the targets have been POD
processed, while the links have not -- except for E<sol> and
E<verbar>. So, if the target contains S<>, the link *must not*.