title: Boost_LIBRARYDIR is not the correct spelling
body: <p>I am trying to add boost to my CMakeLists.txt file. However, I am getting this error:</p>
  
  <pre><code>CMake Error at /export/home/yhe/local/share/cmake-3.3/Modules/FindBoost.cmake:393 (message):
    ERROR: Boost_LIBRARYDIR is not the correct spelling.  The proper spelling
    is BOOST_LIBRARYDIR.
  </code></pre>
  
  <p>I am using cmake3.3.2 and command:</p>
  
  <pre><code>find_package(Boost 1.55.0 COMPONENTS atomic REQUIRED)
  </code></pre>
  
  <p>This is the file:</p>
  
  <pre><code>  1 cmake_minimum_required(VERSION 2.8.9)                                                                                                                                                                         
    2 SET(CMAKE_INCLUDE_DIR ${CMAKE_LINCLUDE_DIR} "/export/home/thirdparty/boost/1.55.0/")                                                                                                                          
    3 SET(CMAKE_LIBRARYDIR ${CMAKE_LIBRARYDIR} "/export/home/thirdparty/boost/1.55.0/lib/AS5")                                                                                                                      
    4 message(${Boost_LIBRARYDIR})                                                                                                                                                                                  
    5 find_package(Boost COMPONENTS atomic REQUIRED)                                                                                                                                                               
  </code></pre>
  
  <p>It turns out the Boost_LIBRARYDIR was defined when I call cmake. Removing the  CMakeCache.txt file, the problem goes away. I guess I might have set Boost_LIBRARYDIR when I was trying to make it work and it got cached. FindBoost.cmake will exit when Boost_LIBRARYDIR has been defined. However, this error message is really misleading.  </p>