Redesign When Equation Implementation in Backend

[Jens Frenkel]

The current implementation for when equations does not consider the MSL3.2 requirements in an efficient way.

cr = ...
(cr,cr,..) = ...

For example the following when

when cond then

(cr1,cr2) = func(...)

elsewhen cond1 then

cr1 = exp;
cr2 = exp;

end when;

should be lecal modelica but its not efficient supported.