Invalid GetElementPtrInst indices

[Sanghyeon_Seo]

This crashes in CodeGen.

void *test(int *i) {
  short a = 1;
  i += a;
}

[Chris_Lattner]

Fixed, thanks!
http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20071231/003619.html

-Chris