Block unwind leak

[jruderman]

fn useBlock(f: fn~() -> uint) { useBlock({|| 22u }) }
fn main() {
    useBlock({|| 22u });
}

leaks after it runs out of stack space:

leaked memory in rust main loop (3 objects)
Assertion failed: (false), function ~memory_region, file ../src/rt/memory_region.cpp, line 172.

[brson]

This is cute. When I run this my logs show:

rust: task 6662fc0 ran out of stack
rust: task 6662fc0 ran out of stack
rust: task 6662fc0 ran out of stack
rust: task 6662fc0 ran out of stack

What I think is happening is that the task runs out of stack, starts unwinding. In a landing pad it grows the stack again, but it's already spent its stack budget, so runs out of stack again, etc. The landing pads just keep throwing until it hits one that has enough stack, and all the ones that failed leak.

I'm going to try to fix it by removing the stack limit during unwinding. I'm not crazy about that but don't see any other solution besides aborting the runtime when a task runs out of stack.