Update `texinfo_updateSectionMenu.sh':
    
        - Don't use the MANUAL_CHAPTER_DIR variable here. Use `$(dirname
          ${MANUAL_ENTRY})' instead; it is safer.
    
          The MANUAL_CHAPTER_DIR variable, here, is used as base location
          to reach the `chapter-menu.texinfo' definition file. When no
          chapter name is provided to `centos-art.sh' script as non-option
          parameter in the command-line, the value of MANUAL_CHAPTER_DIR
          will be empty as well and path to `chapter-menu.texinfo' file
          will be wrong.
    
          The `$(dirname ${MANUAL_ENTRY})' construction, on the other
          hand, will always return the chapter directory where the section
          entry is stored in. No matter if the chapter information wasn't
          provided to `centos-art.sh' script in the command-line.
    
        - Be sure menu entries won't be duplicated when new menu entries
          are added/updated.