Fixed problem with certain term - reworked Simplify a bit

J. Bucher tested Simplify and noticed that

((4-x^5) (3 y^4))/(2.5 x y^3)

was simplified to

((4-x^5)×1.2 y^4)/(x y^3)

although it should rather be

(1.2 (4-x^5) y)/x

This fix enables Simplify to transform such terms with a higher
complexity. The result delivered in this revision is

1.2 * (4.0 - (x)^(5.0)) * (x)^(-1.0) * y