optimization request: (-a)*(-b) => a*b

[Sylvain Pion]

While I am at it, I also think the following kind of tests can be optimized:
(-a)>0  => a<0

Am I right ?  Is it doable ?

For those who wonder, those kind of small optimizations would make a very
clean and efficient implementation of interval arithmetic, so it's useful.

-- 
Sylvain