M.E.Digital.Examples fail to run backend

[Martin Sjölund]

loadModel(Modelica,{"3.1"});
res:=buildModel(Modelica.Electrical.Digital.Examples.Multiplexer);

This causes:
Stack overflow! Failing the current function stack chain until the stack overflow signal is caught!
Execution failed!

And a very long trace of - BackendDAETransform.analyseStrongComponentBlock failed to be printed.

[Jens Frenkel]

There is a strong connected sub equation system. Using +d=delayBreakLoop helps to build the model.

Anyway the compiler should not crash and report a Error Message. Maybe: Use +d=delayBreakLoop to break algebraic loop.

[Jens Frenkel]

In the function BackendDAETransform.analyseStrongComponentBlock

for case  BackendDAE.MIXEDEQUATIONSYSTEM there should be a false as last parameter to avoid mixed systems as part of mixed systems. 

for case  BackendDAE.EQUATIONSYSTEM should maybe tested for

false = BackendVariable.hasDiscreteVar(var_lst);

but I am not a mathematician.