Fix a problem in alias analysis. It is about the misinterpretation of "Object".

This problem is exposed by r171325 which is already reverted. It is rather
hard to fabricate a testing case without it.

r171325 should *NOT* be resurrected as it has a potential problem although 
this problem dosen't directly contribute to PR14988.

The bug is tracked by:
  - rdar://13063553, and
  - http://llvm.org/bugs/show_bug.cgi?id=14988

Thank Arnold for coming up a better solution to this problem. After
comparing this solution and my original proposal, I decided to ditch mine.

llvm-svn: 176225