What to do when we detect bridge highjacking

[jkilpatr]

With the introduction of validator set relaying #327 it is now possible to detect that the bridge has been highjacked, but the question becomes what to actaully do when we detect it?

the damage is already done, funds are already stolen. Alerting the chain to this info is of course importnat. But it's not really going to solve any problems.

Chances are a more valuable use of time is to use evidence based slashing more proactively in the relayer.