Allow NickServ to learn hostmasks automatically.

Allow NickServ to learn hostmasks automatically.

src/nickserv.c (nickserv_addmask): Declare early.
  (cmd_oregister): Allow oper to omit fourth parameter, to set no
    hostmask.
  (cmd_auth): On success, add user's hostmask if the account's hostmask
    list is empty.
  (cmd_cookie): Append hostmask to account on successful allowauth.
  (init_nickserv): Update merge command access.
git-archimport-id: srvx@srvx.net--2006/srvx--devo--1.3--patch-72