* cygheap.cc (init_cygheap::etc_changed): New method to signal

	* cygheap.cc (init_cygheap::etc_changed): New method to signal
	a change in /etc.
	* cygheap.h (struct init_cygheap): Add member `etc_changed_h'
	and method `etc_changed'.
	* grp.cc (enum grp_state): Eliminate.
	(class grp_check): Ditto.
	(group_state): Define as `class pwdgrp_check'.
	(parse_grp): Remeber path and modification time of /etc/group file.
	* passwd.cc (enum_pwd_state): Eliminate.
	(class pwd_check): Ditto.
	(passwd_state): Define as `class pwdgrp_check'.
	(read_etc_passwd): Remember path and modification time of /etc/passwd
	file.
	* pwdgrp.h: New file.
	(enum pwdgrp_state): Substitutes `pwd_state' and `grp_state'.
	(class pwdgrp_check): Substitutes `pwd_check' and `grp_check'.