fix and update mexopencv.make
fix and update mexopencv.make

A new flag was added "opencv_contrib", which indicates whether
optional OpenCV modules are available or not.

Also it now handles "mexopencv_features2d.cpp" used by
MEX-functions wrapping Features2D-derived classes.

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