scoping not handled correctly in the presence of exceptions

[lutzhamel]

Scoping not handled correctly in the presence of exceptions. Consider the following program,

load system io.

function goo with none do
   throw Error("exception").
end

function foo with none do
   let a = 1.
   try
      goo().
   catch _ do
      io @println "exception caught".
   end
   assert(a==1).  -- a no longer in scope
end

foo ().

The nested function goo throws an exception. When the exception is caught scoping no longer works correctly - a is no longer in scope.