Added back logic in patch r46361 (http://llvm.org/viewvc/llvm-project?rev=46361&view...

Added back logic in patch r46361 (http://llvm.org/viewvc/llvm-project?rev=46361&view=rev) with the addition of
some previously missing NULL pointer checks.

Modified the UninitializedValues analysis to not expect that every Expr* at the
block-level is a block-level expression (we probably need to change the name of
such expressions to something truer to their meaning).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@46380 91177308-0d34-0410-b5e6-96231b3b80d8