jansson: change function test to be sure of version

configure.ac

@@ -569,11 +569,11 @@ AC_INIT(configure.ac)
             LDFLAGS="${LDFLAGS}  -L${with_libjansson_libraries}"
         fi
 
-	    AC_CHECK_LIB(jansson, json_loads,, JANSSON="no")
+	    AC_CHECK_LIB(jansson, json_dump_callback,, JANSSON="no")
         enable_jansson="yes"
         if test "$JANSSON" = "no"; then
             echo
-            echo "   Jansson is required for features like unix socket"
+            echo "   Jansson >= 2.2 is required for features like unix socket"
             echo "   Go get it from your distribution of from:"
 	        echo "     http://www.digip.org/jansson/"
             echo