By Tom Miles GENEVA (Reuters) - War crimes blamed on the Syrian opposition are predominantly being carried out by foreign fighters, a U.N. human rights investigator said on Monday, highlighting a deepening rift in the opposition that has been an obstacle to peace talks. "If you're going to look for the (opposition) groups that are committing the worst crimes, look particularly for the foreign fighters, where the foreign fighters are fighting," Karen Koning Abuzayd told reporters in Geneva. ...