Revision 187916

- Rename adding_user(8) to adding_user(7). There's no adding_user utility,
  but the man page describes conceptual information about the process of
  adding a user, thus it should belong to section 7.
- Remove HISTORY and BUGS sections because of the aforementioned reason.

PR:		docs/130151
Submitted by:	Marian Cerny <jojo@matfyz.cz>
MFC after:	3 days