title: find_package() doesn't detect boost on Windows Cmake
body: <p>I'm using a windows system. I want to use the Boost library using CMake.
  I've installed boost on C:\boost_1_55_0\
  Here is my CMakeLists.txt file</p>
  
  <pre><code>set(Boost_USE_STATIC_LIBS        ON)
  set(Boost_USE_MULTITHREADED      ON)
  set(Boost_USE_STATIC_RUNTIME    OFF)
  find_package(Boost 1.55.0 COMPONENTS thread)
  
  if(Boost_FOUND)
      include_directories(${Boost_INCLUDE_DIRS}) 
      LINK_DIRECTORIES(${Boost_LIBRARY_DIRS})
      add_executable (linking_with_boost main.cc sqr.cc)
      target_link_libraries(linking_with_boost ${Boost_LIBRARIES})
  else()
      message(STATUS "Fail  asdasd!")
  endif()
  </code></pre>
  
  <p>I'm getting --Could NOT find Boost
  Output:</p>
  
  <pre><code>$ cmake ../
  -- Could NOT find Boost
  -- Fail  asdasd!
  -- Configuring done
  -- Generating done
  -- Build files have been written to: D:/ubuntu_share/programming/C++/practice/cm
  ake/linking_with_boost/build_win
  </code></pre>