FindBoost: Search for upstream-packaged libs next to includes

Upstream packages Boost binaries for Windows with the 'boost' directory
(the INCLUDE_DIR) next to the lib-... directory (the LIBRARY_DIR).

Modules/FindBoost.cmake

@@ -1496,6 +1496,7 @@ foreach(c DEBUG RELEASE)
       ${Boost_INCLUDE_DIR}/stage/lib
       )
     _Boost_UPDATE_WINDOWS_LIBRARY_SEARCH_DIRS_WITH_PREBUILT_PATHS(_boost_LIBRARY_SEARCH_DIRS_${c} "${Boost_INCLUDE_DIR}/..")
+    _Boost_UPDATE_WINDOWS_LIBRARY_SEARCH_DIRS_WITH_PREBUILT_PATHS(_boost_LIBRARY_SEARCH_DIRS_${c} "${Boost_INCLUDE_DIR}")
     if( Boost_NO_SYSTEM_PATHS )
       list(APPEND _boost_LIBRARY_SEARCH_DIRS_${c} NO_CMAKE_SYSTEM_PATH NO_SYSTEM_ENVIRONMENT_PATH)
     else()