title: cmake: install opencv using external libjpeg library
body: <p>I have two versions of libjpeg library. One is the system library <code>/usr/lib/x86_64-linux-gnu/libjpeg.so</code>, and the another is the newer one that I have built manually <code>/vol/me/lib/libjpeg.so</code>. I want to install <code>opencv</code> that uses the new library instead of the system one. How can I use cmake/cmake-gui to do that?</p>