pkginfo: read locale from environment relying on gettext library. Refs #2694

- Rely on CompsObj base class for groups sorting
pkginfo: new compsdump command. Refs #2694

- The "compsdump" command shows both yum groups and categories.

- Groups and categories are sorted with the yum library method (see
  CompsObj class).

- The old "grouplist" command is retained for backward compatibility.
pkgaction: avoid dereferencing None object. Refs #2694