* Protesters say one person killed after Chadians open fire
* African mission confirms Chadians involved in clash
* MSF says 40 people injured in stampede (Adds Tiangaye press conference)
By Paul-Marin Ngoupana
BANGUI, Dec 23 (Reuters) - Chadian peacekeepers opened fire on a crowd demonstrating against their presence in the capital of Central African Republic on Monday, killing one ...