Add a few C++ helper classes/macros.

Add a few C++ helper classes/macros.

- Macros to disable copying and/or assignment for a class. Although we
  don't want to use macros in general, I think for this purpose the
  macros actually make the code more readable (and also easier to
  write).
- Simple smart pointer class (that wraps boost::scoped_ptr) to help
  manage private implementation classes.  In addition to managing the
  memory and flagging common errors (like boost::scoped_ptr already
  does), it makes the compiler issue errors when the implementation
  class is modified in a const method.

Took them into use throughout the C++ code and fixed a few constness
issues.

Change-Id: Ifa9654e3a4c1979c15457ad07f7bf0462e13472f