* grp.cc (read_etc_group): On NT, add a line for gid = -1. Change name

* grp.cc (read_etc_group): On NT, add a line for gid = -1.  Change name
"unknown" to "mkgroup".
(internal_getgrgid): Do not return default in nontsec case.
(internal_getgroups): Add argument srchsid and look for it in groups if not
NULL.
* passwd.cc (read_etc_passwd): On NT, add a line for uid = -1.  Use same
default uid for Win95 and NT.  Call cygheap_user::ontherange to initialize
HOME.
* cygheap.cc (init_cygheap::etc_changed): Move to uinfo.cc.
* cygheap.h (init_cygheap::etc_changed_h): Remove.
(init_cygheap::etc_changed): Ditto.
* grp.cc (group_state): Remove.  Use gr instead throughout.
(gr): Define as class pwdgrp.
(read_etc_group): Remove gr definition.  Remove calls to set_last_modified and
close.  Pass add_grp to gr.load to load file.
* passwd.cc (passwd_state): Remove.  Use pr instead, throughout.
(pr): Define as class pwdgrp.
(read_etc_passwd): Remove pr definition.  Remove calls to set_last_modified and
close.  Pass add_pwd_line to pr.load to load file.
* pwdgrp.h (etc): New helper class for pwdgrp.
(pwdgrp): Combine pwdgrp_check and pwdgrp_read into one class.  Remove file_w32
and last_modified fields.
(pwdgrp::set_last_modified): Remove.
(pwdgrp::isinitializing): Remove FindFirstFile stuff.  Move to
etc::file_changed.
(pwdgrp::load): Rename from 'open'.  Call etc::init to initialize etc scanning.
Close file handle after reading buffer into memory.  Parse buffer by calling
second argument.
(pwdgrp::gets): Reorganize slightly to rely on eptr starting at beginning of
buffer.  Free buffer when memory exhausted.
(pwdgrp::close): Remove.
* uinfo.cc (etc::dir_changed): New function.
(etc::init): Ditto.
(etc::file_changed): Ditto.
(etc::set_last_modified): Ditto.