Makefile: Define HAVE_UNSAFE for the pre-processor only if HAVE_UNSAFE is
defined in the environment.

Signed-off-by: Kaushik Srenevasan <kaushik@twitter.com>
Use Unsafe.getLong to fetch the layout helper in Java code. Use an
alternate entrypoint that takes the size of the object in question in Heapster.

Signed-off-by: Kaushik Srenevasan <kaushik@twitter.com>