[analyzer] Make ObjCDeallocChecker path sensitive.

[analyzer] Make ObjCDeallocChecker path sensitive.

Convert the ObjCDeallocChecker to be path sensitive. The primary
motivation for this change is to prevent false positives when -dealloc calls
helper invalidation methods to release instance variables, but it additionally
improves precision when -dealloc contains control flow. It also reduces the need
for pattern matching. The check for missing -dealloc methods remains AST-based.

Part of rdar://problem/6927496

Differential Revision: http://reviews.llvm.org/D17511

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@261917 91177308-0d34-0410-b5e6-96231b3b80d8