Use the newly serialized tokens instead of hitting disk (ROOT-6942).

(cherry picked from commit 9320dc8977dd7b8a1acea8b0563495b7c52b4d6c)
Use Module::getNamedValue() to check for existing symbols (ROOT-6909).

(cherry picked from commit b898c73b6d9d88c8c61deba12599b02dfad2c0a8)