Time values were compared as strings. This led to a wrong comparison
result when comparing values one of which is under 100 hours and another is
over 100 hours.

Now when the Arg_comparator::set_cmp_func function sees that both items to
compare are of the TIME type it sets the comparator to the
Arg_comparator::compare_e_int or the Arg_comparator::compare_int_unsigned
functions.