gmmproc: _CLASS_BOXEDTYPE_STATIC: Add copy operations.
gmmproc: _CLASS_BOXEDTYPE_STATIC: Add copy operations.

These were previously implicitly generated by the compiler,
but are no longer generated because we now have explicit move
operations.
Being explicit seems like a better way to preserve ABI anyway.

GNOME/glibmm,GNOME/glibmm,GNOME/glibmm,GNOME/glibmm,GNOME/glibmm