Added color conversion code for older opencv
Added color conversion code for older opencv

nanit/mexopencv,fengzhyuan/mexopencv,CVML/mexopencv,bearpaw/mexopencv,ninghang/opencvmex,ninghang/opencvmex,CVML/mexopencv,nanit/mexopencv,bearpaw/mexopencv,fengzhyuan/mexopencv