Add better consistency check and error output to plot script.

tools/plot-timer-events

 #!/bin/sh
 
 # find the name of the log file to process, it must not start with a dash.
 log_file="v8.log"
 for arg in "$@"
 do
   if ! expr "X${arg}" : "^X-" > /dev/null; then
     log_file=${arg}
   fi
 done
@@ skipping 49 matching lines @@
   options+=`echo "1000*(($t_1_end - $t_1_start) - ($t_2_end - $t_2_start)) \
               / ($n_1 - $n_2)" | bc`
   echo $options
 fi
 
 cat $log_file |
     $d8_exec $tools_path/csvparser.js $tools_path/splaytree.js \
     $tools_path/codemap.js $tools_path/profile.js $tools_path/profile_view.js \
     $tools_path/logreader.js $tools_path/tickprocessor.js \
     $tools_path/profviz/composer.js $tools_path/profviz/stdio.js \
-    -- $@ $options 2>/dev/null | gnuplot > timer-events.png
+    -- $@ $options 2>/dev/null > timer-events.plot
+
+success=$?
+if [[ $success != 0 ]] ; then
+    cat timer-events.plot
+else
+    cat timer-events.plot | gnuplot > timer-events.png
+fi
+
+rm -f timer-events.plot