#1222 fixed (ModelicaTest.Fluid.TestComponents.Vessels.TestInitialization does not initialize)
Removed the fix from r6885.
Rewrote Modelica.Fluid.Vessels.BaseClasses.PartialLumpedVessel according to a suggestion from Hans so that the mixed system of equation can be easier solved/analyzed by a tool by using Boolean variables (and not expressions) in the critical if-clause

git-svn-id: https://svn.modelica.org/projects/Modelica/trunk@6889 7ce873d0-865f-4ce7-a662-4bb36ea78beb