LLVM assertion failure with self-referential struct

[catamorphism]

@am0d reported that this code: https://gist.github.com/3885764 causes this assertion failure:

Assertion failed: (Ty->isSized() && "Cannot getTypeInfo() on a type that is unsized!")```

The assertion failure is the same as in #2718, but it must be at least a slightly different bug, as the test for #2718 passes.

If I change the struct definition in the code to:

struct Tree {
    mut leftTree: Option<@Tree>,
    mut rightTree: Option<@Tree>,
    key: int
}

it compiles successfully.

[nikomatsakis]

For easier reference, here is a test which fails that should work, afaict:

struct Tree {
leftTree: @Option<Tree>,
rightTree: @Option<Tree>,
key: int
}

fn main() {
    let t = Tree {leftTree: @None, rightTree: @None, key: 0};
}

[nikomatsakis]

Not critical for 0.6; removing milestone

[catamorphism]

This might be a dup, but if not, nominating for milestone 5 (production-ready)

[jbclements]

appears to work now.