Widen buffer for headers in psql's \watch command.

This is to make sure there's enough room for translated versions of
the message.  HEAD's already addressed this issue, but back-patch a
simple increase in the array size.

Discussion: <20160612145532.GA22965@postgresql.kr>

src/bin/psql/command.c

@@ -2615,7 +2615,7 @@ static bool
 do_watch(PQExpBuffer query_buf, long sleep)
 {
 	printQueryOpt myopt = pset.popt;
-	char		title[50];
+	char		title[256];
 
 	if (!query_buf || query_buf->len <= 0)
 	{