By Matt Siegel SYDNEY (Reuters) - Australian Prime Minister Tony Abbott on Wednesday declined to rule out sending combat troops to support U.S. air strikes in Iraq, amid a growing confrontation with radical Islamists who have seized large swaths of that country and neighboring Syria. Abbott was asked by a journalist whether "boots on the ground" were needed to push back the Islamic State militant group, which on Tuesday released a video purporting to show the beheading of a second American journalist, Steven Sotloff. ...