schhist/schhist2web: correct handling of deferred columns

This fixes two bugs:

- the last column could leave td=true, causing an extra column to be
  erroneously inserted at the beginning of the next row

- a deferred <TD> at the end of the row would be output before $s,
  placing it right after the last thumbnail instead of the end of
  the thumbnail section

Also combines flushing of "td" for all code paths that produce a
difference image.

schhist/schhist2web

@@ -385,11 +385,11 @@ EOF
 
 
 next="$head"
-td=false
 for n in `cd "$dir" && git rev-list $first..HEAD~1` $first; do
     [ -d "$cache/$n/ppm0" ] || continue
     empty=true
     s="<TR>"
+    td=false
     mkdir -p "$out/$next/"{diff,thumb,html,pdf}
     while read m; do
 	a0="$cache/$n/ppm0/$m.ppm"
@@ -418,21 +418,15 @@ for n in `cd "$dir" && git rev-list $first..HEAD~1` $first; do
 		s="$s<IMG src=\"unchanged.png\">"
 		continue
 	    fi
-	    $td && s="$s<TD>"
-	    td=false
 	    pngdiff shrink "$thumb" -f $THUMB_OPTS "$a2" "$b2" "$a0" "$b0" ||
 	      exit
 	    schps2pdf -T BEFORE -T AFTER -o "$pdf" "$aps" "$bps" || exit
 	elif [ -f "$a0" ]; then
-	    $td && s="$s<TD>"
-	    td=false
 	    pngdiff cat "$diff" -f -c 1,0,0 "$a1" "$a1" || exit
 	    pngdiff shrink "$thumb" -f $THUMB_OPTS -c 1,0,0 "$a2" "$a2" ||
 	      exit
 	    schps2pdf -T DELETED -o "$pdf" "$aps" || exit
 	elif [ -f "$b0" ]; then
-	    $td && s="$s<TD>"
-	    td=false
 	    pngdiff cat "$diff" -f -c 0,1,0 "$b1" "$b1" || exit
 	    pngdiff shrink "$thumb" -f $THUMB_OPTS -c 0,1,0 "$b2" "$b2" ||
 	      exit
@@ -440,13 +434,15 @@ for n in `cd "$dir" && git rev-list $first..HEAD~1` $first; do
 	else
 	    continue
 	fi
+	$td && s="$s<TD>"
+	td=false
 	echo "$s"
 	s=
         wrapped_png "$out" "$next" "$m"
 	empty=false
     done < <(ordered_names)
-    $td && echo "<TD>"
     if ! $empty; then
+	$td && s="$s<TD>"
  	echo "$s<TD valign=\"middle\">"
 	commit_entry "$dir" $next
     fi