Optionally use sun.misc.Unsafe to fetch the size of the object being
sampled.

 - Add Makefile changes to preprocess Heapster.java using the C++
   preprocessor.
 - Rename the generated variable names (Heapster_class ->
   generated_Heapster_class) to reflect new names in
   generated/Heapster-inl.h.
 - Add code in Heapster.java to obtain an instance of sun.misc.Unsafe.

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