Add support for AT CATCH location

One good use of Byteman is to inject rules to log the root cause of an exception where existing code does to attach it as Throwable.initalCause. Unfortunately that is more difficult than it needs to be because you need to specify the location by line number (or other indirect method). There also seems to be some issues with accessing the caught exception by name via "$e" or similar.

It would be simpler if there as an AT CATCH location you could specify, which make the caught exception available as $^ (as AT THROW does).