COMP:test Boost version only if an external Boost was found

CMakeLists.txt

@@ -509,11 +509,15 @@ ENDIF(OTB_USE_PQXX)
 # Boost Library
 #-------------------------------
 FIND_PACKAGE(Boost)
-IF(Boost_FOUND AND ( NOT (${Boost_MINOR_VERSION} EQUAL 40)))
-  OPTION(OTB_USE_EXTERNAL_BOOST "Use an outside build of Boost." ON)
-ELSE(Boost_FOUND AND ( NOT (${Boost_MINOR_VERSION} EQUAL 40)))
+IF(Boost_FOUND)
+  IF (NOT (${Boost_MINOR_VERSION} EQUAL 40))
+    OPTION(OTB_USE_EXTERNAL_BOOST "Use an outside build of Boost." ON)
+  ELSE (NOT (${Boost_MINOR_VERSION} EQUAL 40))
+    OPTION(OTB_USE_EXTERNAL_BOOST "Use an outside build of Boost." OFF)
+  ENDIF (NOT (${Boost_MINOR_VERSION} EQUAL 40))
+ELSE(Boost_FOUND)
   OPTION(OTB_USE_EXTERNAL_BOOST "Use an outside build of Boost." OFF)
-ENDIF(Boost_FOUND AND ( NOT (${Boost_MINOR_VERSION} EQUAL 40)))
+ENDIF(Boost_FOUND)
 # Option for internal/external BOOST
 MARK_AS_ADVANCED(OTB_USE_EXTERNAL_BOOST)