* cygheap.h (class cygheap_user): Add psystemroot member and

	* cygheap.h (class cygheap_user): Add psystemroot member and
	env_systemroot method.
	* environ.cc (struct spenv): Add add_always member.
	(spenvs): Accomodate new add_always member.  Add
	cygheap_user::env_systemroot method to SYSTEMROOT entry.
	(build_env): Check add_always member when adding missing environment
	variables from spenvs.
	* uinfo.cc (cygheap_user::env_systemroot): New method.