Reset value of TEXTDOMAIN locally to common functions.
    
    - Previously, common functions didn't reset the TEXTDOMAIN environment
      variable. This made gettext to read the MO file set in the last
      TEXTDOMAIN definition which may not include the translated strings
      for the function in turn. This update changes the common functions
      that make calls to gettext in order to reset the value of TEXTDOMAIN
      environment variable locally to the appropriate package.
    
      Because the TEXTDOMAIN variable is reset locally to common
      functions, the value it has on higher scopes isn't affected by this
      local reset. This way, it is possible to separate localization of
      modules from localization of common functions.