This is similar to VTK's autoinit scheme except that
no definitions need to be passed at compile time.
It will not work with statically-compiled external
libraries implementing bridges (unlike VTK's autoinit,
which will work at the expense of complexity).

Registration relies on the the C++ specification's
initialization order:

+ static variables with const initializers,
+ static variables with static initializers (BRepModel::s_bridges),
+ static variables with either no initializer or
  dynamic initializers (autoinit objects).