* Response to U.N. appeal last month for $6.5 bln in 2014
* Civil war has rolled back development by 35 years
* U.N.'s Ban hopes peace talks lead to transitional govt
By Sylvia Westall and Warren Strobel
KUWAIT, Jan 15 (Reuters) - Western and Gulf Arab nations pledged more than $2.4 billion on Wednesday for U.N. aid efforts in Syria, where a near three-year civil war has left ...