Compiling OpenCV from Source Excluding Features

I'm trying to install OpenCV 3.1.0 from source on OSX following this article. Long story short, I'm at the point of creating the make file using the following declarations:

cmake -D CMAKE_BUILD_TYPE=RELEASE -D CMAKE_INSTALL_PREFIX=/usr/local 
-D PYTHON2_PACKAGES_PATH=~/.virtualenvs/cv/lib/python2.7/site-packages 
-D PYTHON2_LIBRARY=/usr/local/Cellar/python/2.7.11/Frameworks/Python.framework/Versions/2.7/bin 
-D PYTHON2_INCLUDE_DIR=/usr/local/Frameworks/Python.framework/Headers 
-D INSTALL_C_EXAMPLES=OFF -D INSTALL_PYTHON_EXAMPLES=ON 
-D BUILD_EXAMPELS=ON 
-D OPENCV_EXTRA_MODULES_PATH=~/opencv_contrib/modules ..

The resultant build information I get includes this:

    --   OpenCV modules:
    --     To be built:                 core flann imgproc ml photo reg
 surface_matching video dnn fuzzy imgcodecs shape videoio highgui objdetect plot
 superres ts xobjdetect xphoto bgsegm bioinspired dpm face features2d
 line_descriptor saliency text calib3d ccalib datasets rgbd stereo
 structured_light tracking videostab xfeatures2d ximgproc aruco optflow
 stitching python2
    --     Disabled:                    world contrib_world
    --     Disabled by dependency:      -
    --     Unavailable:                 cudaarithm cudabgsegm cudacodec cudafeatures2d cudafilters cudaimgproc cudalegacy cudaobjdetect cudaoptflow cudastereo cudawarping cudev java python3 viz cvv hdf matlab sfm

Most notably: xfeatures2d

I then run make -j4 and then sudo make install to install the compiled OpenCV 3.1.0 package. The output includes:

-- Installing: /usr/local/lib/libopencv_xfeatures2d.3.1.0.dylib
-- Up-to-date: /usr/local/lib/libopencv_xfeatures2d.3.1.dylib
-- Up-to-date: /usr/local/lib/libopencv_xfeatures2d.dylib
-- Up-to-date: /usr/local/include/opencv2/xfeatures2d.hpp
-- Up-to-date: /usr/local/include/opencv2/xfeatures2d/cuda.hpp
-- Up-to-date: /usr/local/include/opencv2/xfeatures2d/nonfree.hpp

Immediately after, I run python for the interpreter, then import cv, cv2.xfeatures2d and get:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'module' object has no attribute 'xfeatures2d'

I don't understand why the extra packages added by opencv-contrib aren't being included in the installation. cmake says they're being included, but they aren't.

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