Segfault when running test iterable.an

[jfecher]

After being updated to use the new Vec 't implementation from stdlib the Iterable test crashes when run. Upon a quick analysis, the problem stems from line 13 containing the for loop: "for i in v do ...".

When v is replaced with an immutable Vec, eg. Vec(1..5) the program runs fine. The crash seems to be an issue with creating a VecIter i32 object from a mut Vec i32 object. A quick look at the IR generated with -emit-llvm shows some oddities with the type inference of VecIter being VecIter (mut i32), although nothing immediately stands out as crash worthy.