Generic vector reads read from the wrong place

[pcwalton]

Test case:

fn get[T](vec[T] v) -> T {
    ret v.(1);
}

fn main() {
    auto v = vec(1, 2, 3, 4, 5);
    log get(v);
}

Result:

[pwalton@fireferret ~/Source/rust/build] ./a.out
rt: ---
rt: 12ed:main:main:                       rust: 33554432 (0x2000000)

ret v.(0) works, so looks like we're miscalculating vec element size.

[pcwalton]

Fixed by 7f3f66d.