title: Set minimum version of boost in cmake
body: <p>I want to define a minimum boost version to be available on the system. I tried the following approach. Unfortunately this did not work, as it tries to compile also with only boost 1.40.0 available on the system.</p>
  
  <pre><code>SET(Boost_USE_STATIC_LIBS OFF)
  SET(Boost_USE_MULTITHREAD OFF)
  SET(BOOST_MIN_VERSION "1.47.0")
  
  FIND_PACKAGE(Boost REQUIRED)
  
  FIND_PACKAGE(Boost REQUIRED)
  if (NOT Boost_FOUND)
        message(FATAL_ERROR "Fatal error: Boost (version &gt;= 1.47.0) required.\n")
  endif (NOT Boost_FOUND)
  
  INCLUDE_DIRECTORIES(${Boost_INCLUDE_DIRS})
  LINK_DIRECTORIES(${Boost_LIBRARY_DIRS})
  </code></pre>
  
  <p>How did I get cmake to control the correct boost version, before compiling?</p>