Futures: Fix exception handling

[vpmedia]

ehtest: goes into infinite loop...

< 
< *** catch test 0
< Foo constructor
< throwing Bar
< Bar constructor

---
> throwing Baz
> Baz constructor
> Foo destructor
> caught Baz
> Baz destructor
20345379c21
< *** catch test 0

---
> *** catch test 2
20345381,20345382c23,25
< throwing Bar
< Bar constructor

---
> throwing int (14)
> Foo destructor
> caught int (14)
20345384c27
< *** catch test 0

---
> *** catch test 3
20345386c29
< throwing Bar

---
> throwing long (won't be caught!; 15L)