Simplify: Oscillating behaviour

[Martin Sjölund]

List some expressions that oscillate if we call simplify() twice on the expression. It is not always easy to remove such things, but some of these should be possible to solve.

This should be possible to solve by multiplying the factors instead of swapping them...

simplify:
(x + y * z) * 1.0 / (1.0 - a) / b
=>
(x + y * z) * 1.0 / b / (1.0 - a)
=>
(x + y * z) * 1.0 / (1.0 - a) / b