Qatar-based Al-Jazeera television has aired a video of Al Qaeda number two Ayman al-Zawahiri vowing to avenge the death of the network's Iraq frontman Abu Musab al-Zarqawi. Zarqawi was killed in a United States air raid in Iraq on June 7. In the video, Zawahiri is seated in front of a picture of Zarqawi. He addresses US President George W Bush directly. "Yes O Bush, none of us is killed without us avenging him, with the help of God," he said. "Do you remember, O Bush, how the lion of Islam, the mujahed [holy warrior] Osama bin Laden, God keep...