fix the way we discover OpenCV libs in mexopencv.make
fix the way we discover OpenCV libs in mexopencv.make

in case we dont have both debug and release builds.

bearpaw/mexopencv,nanit/mexopencv,fengzhyuan/mexopencv,CVML/mexopencv,bearpaw/mexopencv,nanit/mexopencv,fengzhyuan/mexopencv,CVML/mexopencv