* stime.c (scm_mktime): take an optional zone argument.

	* stime.c (scm_mktime): take an optional zone argument.
	(scm_localtime): check putenv return value.
	(scm_strftime, scm_strptime): moved from posix.c.  move #include
	sequences.h too.
	stime.h, posix.h: update prototypes.
	(bdtime2c, setzone, restorezone): new static procedures.
	(scm_mktime, scm_strftime): use them.
	(scm_strftime): don't call mktime before strftime.  Use
	filltime for return value.
	(filltime): convert NULL zname to #f.
*	(scm_strptime): return a count of characters consumed, not
	the remaining string.

	* stime.c (scm_localtime): check HAVE_TM_ZONE and HAVE_TZNAME.
	(scm_mktime): likewise.
	Declare *tzname[].
	Uncomment localtime and mktime.

	* configure.in: add AC_STRUCT_TIMEZONE.