* 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.

    * include/dynamic-graph/signal-caster.h,
    * src/signal/signal-caster.cpp.

	 * src/signal/signal-caster.cpp: cut long lines for function
	   SignalCaster::registerCast.

     * src/signal/signal-caster.cpp.

     * include/dynamic-graph/signal-caster.h,
     * src/signal/signal-caster.cpp: if a typename is registered several times,
     throw only if pointers to type_info differ. When loading python modules,
     for some reason, global variables are constructed several times.