By Khalid Abdelaziz KHARTOUM (Reuters) – Sudanese security forces used stun grenades and tear gas on Monday to disperse crowds of protesters rallying in Khartoum on the fourth anniversary of the uprising that toppled former leader Omar al-Bashir, a Reuters reporter said. The protests in the capital come two weeks after the military leaders who staged a coup last year signed an outline deal with political parties to relaunch a transition towards democratic elections with international support. The deal faces major challenges, including limited public backing for the civilian signatories and the…