Backend: Fixed attribute not working properly for variables

[sjoelund.se]

The following two classes will generate different initial equations. In the first case, we will solve r and get der(r) = 1 = r.

class A

Real r(fixed = false, start=2.0);

initial equation

der(r) = 1;

equation

der(r) = r;

end A;

In the second case, r will not be solved for in the initial equations. r = 2; der(r) = 1.

class A

Real r(start=2.0);

initial equation

der(r) = 1;

equation

der(r) = r;

end A;

[wbraun]

works in trunk