Failing dtor leaks fields

[brson]

// error-pattern: fail                                                                                                                                                           
fn main() {
    struct S {
        box: ~int
    }

    impl Drop for S {
        fn drop(&self) { fail!() }
    }

    let s = S { box: ~0 };
}

task <unnamed> failed at 'explicit failure', /home/brian/dev/rust/src/test/run-fail/test.rs:8
==7954== 8 bytes in 1 blocks are definitely lost in loss record 1 of 1
==7954==    at 0x559E58B: malloc (jemalloc.c:906)
==7954==    by 0x4EE69C5: rt::global_heap::malloc_raw::_d4e11475f81475::_0$x2e8$x2dpre (in /opt/dev/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustc/x86_64-unknown-linux-gnu/lib/libstd-6c65cf4b443341b1-0.8-pre.so)
==7954==    by 0x400B27: _rust_main (in /opt/dev/rust/build/x86_64-unknown-linux-gnu/test/run-fail/test.stage1-x86_64-unknown-linux-gnu)
==7954==    by 0x4F687C9: rt::task::__extensions__::build_start_wrapper::anon::anon::expr_fn_29465 (in /opt/dev/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustc/x86_64-unknown-linux-gnu/lib/libstd-6c65cf4b443341b1-0.8-pre.so)
==7954==    by 0x4F67339: rt::task::__extensions__::run::anon::expr_fn_29387 (in /opt/dev/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustc/x86_64-unknown-linux-gnu/lib/libstd-6c65cf4b443341b1-0.8-pre.so)
==7954==    by 0x5590E0E: rust_try (rust_builtin.cpp:520)
==7954==    by 0x4F671D7: rt::task::__extensions__::meth_29385::try::_199ab8d6eb226980::_0$x2e8$x2dpre (in /opt/dev/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustc/x86_64-unknown-linux-gnu/lib/libstd-6c65cf4b443341b1-0.8-pre.so)
==7954==    by 0x4F67098: rt::task::__extensions__::meth_29383::run::_199ab8d6eb226980::_0$x2e8$x2dpre (in /opt/dev/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustc/x86_64-unknown-linux-gnu/lib/libstd-6c65cf4b443341b1-0.8-pre.so)
==7954==    by 0x4F684AA: rt::task::__extensions__::build_start_wrapper::anon::expr_fn_29449 (in /opt/dev/rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustc/x86_64-unknown-linux-gnu/lib/libstd-6c65cf4b443341b1-0.8-pre.so)
==7954==

[thestinger]

Fixed by #10219.