Enhance IS_LOADABLE_DYN and LOAD_DYN to also check that the garbage collector matches

[fingolfin]

Thanks to a clever idea by @ChrisJefferson kernel extensions these days are checked for using an ABI version compatible with the active GAP kernel. This is done by a little hack using the type field of StructInitInfo to encode the version:

    // info->type should not be larger than kernel version
    if (info->type / 10 > GAP_KERNEL_API_VERSION)
        return False;

    // info->type should not have an older major version
    if (info->type / 10000 < GAP_KERNEL_MAJOR_VERSION)
        return False;

    // info->type % 10 should be 0, 1 or 2, for the 3 types of module
    if (info->type % 10 > 2)
        return False;

    return True;

Perhaps we can use a few more bits of that to also store which GC was used to compile the kext (say 0=GASMAN, 1=Julia, 2=Boehm). Then we would be able to avoid loading kexts into a kernel which has the right version but different GC implementation.