title: Boost_LIBRARIES doesn't contain program_options
body: <p>When building my project, Boost_LIBRARIES doesn't contain program_options even though it is required and found. If I add it manually, it works fine. My CMake contains the following:</p>
  
  <pre><code>find_package(Boost 1.60.0 REQUIRED COMPONENTS program_options thread system regex)
  message("${Boost_LIBRARIES}")
  include_directories(include ${Boost_INCLUDE_DIRS})
  link_directories(${Boost_LIBRARY_DIRS})
  target_link_libraries (proj ${Boost_LIBRARIES} boost_program_options)
  </code></pre>
  
  <p>CMake claims that the library was found, but it is not listed in the call to <code>message("${Boost_LIBRARIES}")</code></p>