Compilation : fix oqgraph's system check, in case where boost header aren't in...

Compilation : fix oqgraph's system check, in case where boost header aren't in standard include directory.

storage/oqgraph/CMakeLists.txt

@@ -3,6 +3,7 @@ IF(NOT Boost_FOUND)
   RETURN()
 ENDIF()
 INCLUDE_DIRECTORIES(BEFORE ${Boost_INCLUDE_DIRS})
+SET(CMAKE_REQUIRED_INCLUDES ${CMAKE_REQUIRED_INCLUDES} ${Boost_INCLUDE_DIRS})
 
 IF(MSVC)
   # lp:756966 OQGRAPH on Win64 does not compile