Asteroid specific stack trace when an uncaught Asteroid Exception is thrown

[lutzhamel]

Asteroid specific stack trace when an uncaught Asteroid Exception is thrown rather than a generic Python trace.

[lutzhamel]

Unchecked Asteroid exceptions now trigger a backtrace. For example, the
following program,

function divide with (dividend, divisor) do
   return divide2(dividend,divisor).
end

function divide2 with (dividend, divisor) do
   return dividend/divisor.
end

let i = divide(3,0).

will give rise to the trace back,

traceback (most recent call last):
except.ast: 1: calling <toplevel>
except.ast: 9: calling divide
except.ast: 2: calling divide2
error: except.ast: 6: integer division or modulo by zero