- introduced manual selection of tearing variables using annotations …

…(works only for cellier tearing heuristic MC3 yet)

  -> attributes:
     tearingSelect = always: variable is forced to be iteration variable
     tearingSelect = prefer: variable gets better chances to become iteration variable
     tearingSelect = avoid:  variable gets less chances to become iteration variable
     tearingSelect = never:  variable won't be iteration variable as long as it is possible to solve for it algebraically (otherwise: warning)

example:
model AnnotationTest
   Real u0;
   Real i1 annotation(tearingSelect=prefer);
   Real i2; 
   Real i3; 
   Real u1; 
   Real u2 annotation(tearingSelect=avoid);
   Real u3;
   ...   
	 
- added testmodels with manual tearing selection



git-svn-id: https://openmodelica.org/svn/OpenModelica/trunk@20929 f25d12d1-65f4-0310-ae8a-bbce733d8d8e