title: Wrong python packages path for opencv cmake installation
body: <p>I've been trying to follow the opencv installation steps from <a href="http://www.pyimagesearch.com/2015/06/15/install-opencv-3-0-and-python-2-7-on-osx/" rel="noreferrer">pyimagesearch.com</a> with virtualenv. Everything works fine except for the packages path: it should be <code>/Users/JLee/Envs/cv/lib/python2.7/site-packages</code> but it's configured as <code>lib/python2.7/site-packages</code></p>
  
  <p>In Python, <code>import cv2</code> works well in the global setting but doesn't work in the 'cv' virtual environment. </p>
  
  <p>While following the steps from the site, I first proceeded without installing virtualenv, then realized I haven't installed it so I installed it later and followed the steps again. Could this be a problem? </p>
  
  <pre><code> Python 2:
  --     Interpreter:                 /Users/JLee/Envs/cv/bin/python2.7 (ver 2.7.10)
  --     Libraries:                   /usr/lib/libpython2.7.dylib (ver 2.7.10)
  --     numpy:                       /Users/JLee/Envs/cv/lib/python2.7/site-packages/numpy/core/include (ver 1.11.1)
  --     packages path:               lib/python2.7/site-packages
  </code></pre>
  
  <p>This is the code for cmake to configure the build:</p>
  
  <pre><code>cmake -D CMAKE_BUILD_TYPE=RELEASE 
  -D CMAKE_INSTALL_PREFIX=/usr/local \ 
  -D PYTHON2_PACKAGES_PATH=/Users/JLee/Envs/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_EXAMPLES=ON \ 
  -D OPENCV_EXTRA_MODULES_PATH=/Users/JLee/Developer/opencv_project/opencv_contrib/modules ..
  </code></pre>
  
  <p>Thanks for the help in advance!</p>