title: CMake: Eigen3 include dirs needed from a third project
body: <p>I've implemented a library which uses Eigen3. The following lines are part of the CMake of this library:</p>
  
  <pre><code>#EIGEN
  find_package(Eigen3 REQUIRED) 
  include_directories(${EIGEN3_INCLUDE_DIR})
  </code></pre>
  
  <p>And Eigen3 is found and my library compiles without any problem.</p>
  
  <p>The complication appears when I use my library in other project. This project has nothing to be with Eigen, it is not used there. However, if I don't include the Eigen include dirs in this project as well, its compilation fails.</p>
  
  <p>My library is compiled as a dynamic one, and I guess some Eigen stuff is missing from it, and that's why the project needs Eigen include directories as well. Any idea about how to fix this?</p>
  
  <p>Thank you.</p>
  
  <p>PS: I'm in Ubuntu 13.04 and using QtCreator as IDE.</p>