Sync our copy of the timezone library with IANA release tzcode2016g.

This is mostly to absorb some corner-case fixes in zic for year-2037
timestamps.  The other changes that have been made are unlikely to affect
our usage, but nonetheless we may as well take 'em.

src/timezone/localtime.c

@@ -1280,9 +1280,8 @@ gmtsub(pg_time_t const * timep, int32 offset, struct pg_tm * tmp)
 	result = timesub(timep, offset, gmtptr, tmp);
 
 	/*
-	 * Could get fancy here and deliver something such as "UT+xxxx" or
-	 * "UT-xxxx" if offset is non-zero, but this is no time for a treasure
-	 * hunt.
+	 * Could get fancy here and deliver something such as "+xx" or "-xx" if
+	 * offset is non-zero, but this is no time for a treasure hunt.
 	 */
 	if (offset != 0)
 		tmp->tm_zone = wildabbr;

src/timezone/private.h

@@ -23,6 +23,7 @@
 
 #include "pgtime.h"
 
+/* This string was in the Factory zone through version 2016f.  */
 #define GRANDPARENTED	"Local time zone must be set--see zic manual page"
 
 /*

src/timezone/strftime.c

@@ -128,7 +128,7 @@ pg_strftime(char *s, size_t maxsize, const char *format,
 	int			warn;
 
 	warn = IN_NONE;
-	p = _fmt(((format == NULL) ? "%c" : format), t, s, s + maxsize, &warn);
+	p = _fmt(format, t, s, s + maxsize, &warn);
 	if (p == s + maxsize)
 		return 0;
 	*p = '\0';