[analyzer] Let TK_PreserveContents span across the whole base region.

If an address of a field is passed through a const pointer,
the whole structure's base region should receive the
TK_PreserveContents trait and avoid invalidation.

Additionally, include a few FIXME tests shown up during testing.

Differential Revision: http://reviews.llvm.org/D19057

llvm-svn: 267413