tzselect better signals wrong UTC clocks

Problem reported by Robert Elz in:
https://mm.icann.org/pipermail/tz/2023-January/032533.html
* tzselect.ksh: Tell user the system’s UTC timestamp and ask them
to assume that it’s correct when selecting the local time.
This should warn users better if the UTC clock is wrong.
Also, use ‘TZ=UTC0 date’ rather than ‘date -u’ for consistency
with how ‘date’ is used elsewhere in this script.

tzselect.ksh

@@ -487,7 +487,8 @@ while
 		*)
 		case $continent in
 		time)
-		  old_minute=`date -u +%Y%m%d%H%M`
+		  minute_format='%a %b %d %H:%M'
+		  old_minute=`TZ=UTC0 date +"$minute_format"`
 		  for i in 1 2 3
 		  do
 		    time_table_command=`
@@ -495,13 +496,14 @@ while
 			  "$output_distances_or_times" <"$TZ_ZONE_TABLE"
 		    `
 		    time_table=`eval "$time_table_command"`
-		    new_minute=`date -u +%Y%m%d%H%M`
+		    new_minute=`TZ=UTC0 date +"$minute_format"`
 		    case $old_minute in
 		    "$new_minute") break;;
 		    esac
 		    old_minute=$new_minute
 		  done
-		  echo >&2 'What is the current date and 24-hour time?'
+		  echo >&2 "The system says Universal Time is $new_minute."
+		  echo >&2 "Assuming that's correct, what is the local time?"
 		  eval doselect `
 		    say "$time_table" |
 		    sort -k2n -k2,5 -k1n |