Check for algorithm/external section

[Martin Sjölund]

Using inheritance, it is possible to get both algorithm section and external declaration in the DAE. Fix this :)

{{{model M

function funky

output Real y;

algorithm

y := 1.0;

end funky;
function sin

input Real x;
extends funky;

external "C" y=sin(x);
end sin;
Real x = sin(time);

end M;}}}

Also check for initial algorithm.