Call to g_caster function have been replaced by call to
    SignalCaster::getInstance.

    g_pool and g_factory global variables have been replaced by static methods
    getInstance in each class.
    getInstance returns a pointer to the unique instance of the class and
    creates it if needed.

  This virtual methods is defined in Entity class. Changing the prototype
  breaks the overloading mecanism.

Code cleaning after rewriting (marginal) of sig-cast. Introduction of a specific tracer behaviour for matrix and vector.

      Remove pool::getSignal().

       This reverts commit 8fca0b1a.
       Move python interpreter in dynamic-graph-python.

    * include/dynamic-graph/interpreter.h,
    * src/CMakeLists.txt,
    * src/dgraph/interpreter.cpp,
    * tests/CMakeLists.txt,
    * tools/dg-python.cpp: new,
    * tools/CMakeLists.txt: this adds a dependency to  python in dynamic-graph.