sum(...)
PROTOTYPE: @
CODE:
{
    SV *sv;
    int index;
    if(!items) {
        XSRETURN_UNDEF;
    }
    sv = ST(0);
    RETVAL = slu_sv_value(sv);
    for(index = 1 ; index < items ; index++) {
        sv = ST(index);
        RETVAL += slu_sv_value(sv);
    }
}
OUTPUT:
    RETVAL