* external.cc (cygwin_internal): Use security_descriptor::copy method.

	* external.cc (cygwin_internal): Use security_descriptor::copy method.
	* sec_helper.cc (security_descriptor::malloc): Use own free method.
	Set type.
	(security_descriptor::realloc): Handle the case that psd has been
	allocated using LocalAlloc.  Set type.
	(security_descriptor::free): Ditto.
	* security.cc (get_nt_attribute): Remove.
	(get_reg_security): Remove.
	(get_nt_object_security): Use GetSecurityInfo which handles all
	securable objects.
	(get_nt_object_attribute): Remove.
	(get_object_attribute): Call get_nt_object_security instead of
	get_nt_object_attribute.
	(get_file_attribute): Ditto.
	(check_registry_access): Call get_nt_object_security instead of
	get_reg_security.
	* security.h (cygpsid::operator PSID): Make method const, not the
	result.
	(class security_descriptor): Add type member.  Accomodate throughout.
	(security_descriptor::copy): New method.
	(security_descriptor::operator PSECURITY_DESCRIPTOR *): New operator.