Pointed out by A. Mallet.

This crashes the linkage because of the particular link
with the frameworks (here the framework Acceleration).

    Patch reported by Anthony Mallet.

This solution worked only for win32 systems, and
created link errors for unix systems...

This reverts commit e7e487ebdf9c550742d4c9525bbb151e25437393.

    Call to g_caster function have been replaced by call to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    g_pool and g_factory global variables have been replaced by static methods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.

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