Actually intercept free() to ensure that the deallocations caused by other...

Actually intercept free() to ensure that the deallocations caused by other functions directly calling it are routed to our allocator.
For the allocations that do not belong to any malloc zone check whether they're padded with a pointer to ASan's CFAllocator. If so, free the original (unpadded) pointer.
This should fix AddressSanitizerMac.NSURLDeallocation and issue 70.

llvm-svn: 158863