Revision 188072

MFC: r187916
  - 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>