Simplify Iteratee.recover* methods; rename IterateeExeption to IterateeException
Remove volatile var from trampoline

Change variable names to make it clear that we don't need a
`var`. Use a match expression so that local.get's value isn't
in scope when it has a null value.
Merge pull request #3623 from richdougherty/misc-iteratee

Remove volatile var from trampoline; simplify Iteratee.recover* methods