[boost] everything is [rational]

whenever we do arithmetic, we are doing some kind of rational arithmetic: - integer arithmetic is rational arithmetic with all denominators equal to 1 - fixed point arithmetic is rational arithmetic with all denominators being a pre-specified constant - floating point arithmetic is rational arithmetic with denominator values limited to powers of 2 (e.g. 1/3 is represented as 11184811/2^25) - finite rational<> arithmetic is rational arithmetic with denominator values limited to a given range the first three does rounding, so the rule of thumb "behave like int" suggests rational<> should do the same. if we do not do rounding, we have to have some very good reasons for not doing it. br, andras