add two simple test cases for tree rotation, 1 possible, 1 impossible
add two simple test cases for tree rotation, 1 possible, 1 impossible

BioInf-Wuerzburg/AliTV,BioInf-Wuerzburg/AliTV,BioInf-Wuerzburg/AliTV,AliTVTeam/AliTV,BioInf-Wuerzburg/AliTV,BioInf-Wuerzburg/AliTV,BioInf-Wuerzburg/AliTV,AliTVTeam/AliTV