[analyzer] Use optimized assumeDual for branches.
[analyzer] Use optimized assumeDual for branches.

This doesn't seem to make much of a difference in practice, but it does
have the potential to avoid a trip through the constraint manager.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@169524 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang