* uinfo.cc (pwdgrp::next_str): Search only for input char in string. Return
EOS on failure. Don't check for NULL since it shouldn't be possible.
(pwdgrp::add_line): Revert to replacing '\n' in input line with '\0'.
(pwdgrp::next_num): Pass explicit separator character to next_str.
* grp.cc (pwdgrp::parse_group): Ditto.
* passwd.cc (pwdgrp::parse_passwd): Ditto. Revamp test for garbage input.
* pwdgrp.h (pwdgrp::next_str): Don't use default parameter.