Backend: Sorting simple equations and algorithm sections

[Martin Sjölund]

The following generates wrong code (h = 0 after initialization, and the first time step causes derx=x=NaN)

The problem is that code for simple equations and algorithms are generated separately, which means it can't possibly handle even harder models.

model A
Real x(start=37);
Real derx;
Real h = 0.01; // time step
algorithm
// x=15+time, der(x)=??? weird during init due to start being wrong?
derx := (15+time-x)/h;
x := x+derx*h;
end A;