- fixes for bug [#1188] https://openmodelica.org:8443/cb/issue/1188

  Connections.isRoot evaluates to wrong value in Modelica.Mechanics.MultiBody.Examples.Elementary.FreeBody
- the problem was a typo in ConnectionGraph.addBranchesToTable generated a wrong hash table.
- moved public functions in the beginning of ConnectionGraph.mo
- make all functions not accessed from outside be protected in ConnectionGraph.mo
- more testsuite/libraries/multibody/ need updating (will do that with a later commit).

git-svn-id: https://openmodelica.org/svn/OpenModelica/trunk@5279 f25d12d1-65f4-0310-ae8a-bbce733d8d8e