* README: using Automake 1.2d

	* README: using Automake 1.2d
	* configure.in: AC_CHECK_FUNCS: add "system".
	* simpos.c (scm_system): always define: use sysmissing if not
	available.  Check for HAVE_SYSTEM instead of _Windows (does
	Windows lack system or does it have an unusable one?).
	Check for error conditions -1 and 127.  Use SCM_DEFER_INTS.
	Let the argument be optional: if not supplied, call system(NULL).
	* ports.c (scm_close_port): relax the type check from OPPORTP to
	PORTP; closing a closed port is allowed.