* Gunfire rings out across northern town hours after raid
* Resident says troops hunt for attackers
* Bombing underscores lack of security as U.N. force deploys (Adds death of child, number of bombers)
By Adama Diarra
BAMAKO, Oct 23 (Reuters) - A suicide blast killed two Chadian troops from the U.N. mission in Mali and injured six other peacekeepers in an assault on a checkpoint at the ...