COMP: add messages when we look for Boost two times

Modules/ThirdParty/Boost/otb-module-init.cmake

@@ -3,12 +3,14 @@ if (BUILD_TESTING)
 endif()
 
 # Required
+message(STATUS "Looking for required Boost headers")
 find_package ( Boost
   1.35.0
   REQUIRED
   )
 
 # Optional components
+message(STATUS "Looking for optional Boost commponents : ${OTB_Boost_OPTIONAL_COMPONENTS}")
 find_package ( Boost
   1.35.0
   COMPONENTS ${OTB_Boost_OPTIONAL_COMPONENTS}