use better IPOPT variables

CMakeLists.txt

@@ -188,9 +188,9 @@ endif ()
 find_package (IPOPT)
 if (IPOPT_FOUND)
   set (COMISO_IPOPT_CONFIG_FILE_SETTINGS "#define COMISO_IPOPT_AVAILABLE 1" )
-  list( APPEND COMISO_INCLUDE_DIRECTORIES ${IPOPT_INCLUDE_DIR} )
-  list( APPEND COMISO_LINK_DIRECTORIES ${IPOPT_LIBRARY_DIR} )
-  list( APPEND COMISO_LINK_LIBRARIES ${IPOPT_LIBRARY} )
+  list( APPEND COMISO_INCLUDE_DIRECTORIES ${IPOPT_INCLUDE_DIRS} )
+  list( APPEND COMISO_LINK_DIRECTORIES ${IPOPT_LIBRARY_DIRS} )
+  list( APPEND COMISO_LINK_LIBRARIES ${IPOPT_LIBRARIES} )
   if ( IPOPT_HSL_LIBRARY_DIR )
 	set (COMISO_HSL_CONFIG_FILE_SETTINGS "#define COMISO_HSL_AVAILABLE 1" )
   else ()