execute the given execution-token and catch
any exception that can be caught therein.
software can arbitrarily raise an exception
using THROW - the value 0 means there
was no exception, other denote implementation
dependent exception-codes.
raise an exception - it will adjust the depth
of all stacks and start interpreting at the point
of the latest CATCH
if n is null nothing happens, the -1 (ie. FALSE )
is the raise-code of ABORT - the other codes
are implementation dependent and will result in
something quite like ABORT