specilizations for abs math function for int & char
specilizations for abs math function for int & char

abs(int) and abs(char) were always returning zeros on CUDA
backend, probably a bug in CUDA sdk. This change fixes this
behaviour on CUDA backend which effects the following functions:

* af_assign_gen
* af_index_gen

victorv/arrayfire,marbre/arrayfire,victorv/arrayfire,hshindo/arrayfire,9prady9/arrayfire,umar456/arrayfire,hshindo/arrayfire,umar456/arrayfire,pentschev/arrayfire,9prady9/arrayfire,merlin-ext/arrayfire,victorv/arrayfire,ghisvail/arrayfire,arrayfire/arrayfire,ghisvail/arrayfire,hshindo/arrayfire,munnybearz/arrayfire,merlin-ext/arrayfire,hshindo/arrayfire,arrayfire/arrayfire,arrayfire/arrayfire,9prady9/arrayfire,shehzan10/arrayfire,umar456/arrayfire,umar456/arrayfire,arrayfire/arrayfire,bkloppenborg/arrayfire,victorv/arrayfire,munnybearz/arrayfire,bkloppenborg/arrayfire,ghisvail/arrayfire,marbre/arrayfire,9prady9/arrayfire,bkloppenborg/arrayfire,marbre/arrayfire,marbre/arrayfire,shehzan10/arrayfire,pentschev/arrayfire,ghisvail/arrayfire,pentschev/arrayfire,merlin-ext/arrayfire,shehzan10/arrayfire,bkloppenborg/arrayfire,merlin-ext/arrayfire,shehzan10/arrayfire,munnybearz/arrayfire,pentschev/arrayfire