#6 Make Python module of FDNT

The Python interface is working, and I need to wrap up this issue.  This pull request is to remind myself what has been done.

Major changes:
 * scons compilation (easy to deal with compiler differences of different systems)
 * Python / C++ interface with Boost Python
   * `position.py` module: `PositionD` and `PositionI` class
   * `bounds.py` module: 
   * `fdntimage.py` module: `FDNTImage` class (along with `FDNTImageS`, `FDNTImageI`, `FDNTImageF`, `FDNTImageD`)
   * `runfndt.py` module: `FDNTShapeData` class contains the shape measurement results, `RunFDNT()` function
 * A sample Python script: examples/demo1.py 

Sadly, I will be reviewing my own code for now.
It looks like this was an error in the GalSim SConstruct file too.  This line should use `default_cxx`.  I believe that default should be `c++`, rather than `g++`, but on most systems they are the same thing, so it doesn't make much of a difference.