title: How to properly add include directories with CMake
body: <p>About a year ago I asked about <a href="https://stackoverflow.com/questions/7461000/handling-header-files-dependencies-with-cmake">header dependencies in CMake</a>.</p>
  
  <p>I realized recently that the issue seemed to be that CMake considered those header files to be <em>external</em> to the project. At least, when generating a Code::Blocks project the header files do not appear within the project (the source files do). It therefore seems to me that CMake consider those headers to be <em>external</em> to the project, and does not track them in the depends.</p>
  
  <p>A quick search in the CMake tutorial only pointed to <code>include_directories</code> which does not seem to do what I wish...</p>
  
  <p>What is the proper way to signal to CMake that a particular directory contains headers to be included, and that those headers should be tracked by the generated Makefile?</p>