Tweak behavior when executing handheld batch results

redirect to final batch when done, try to warn user a bit

tailbone/templates/batch/handheld/index.mako

@@ -53,6 +53,12 @@ ${parent.body()}
 <div id="execution-options-dialog" style="display: none;">
   ${h.form(url('{}.execute_results'.format(route_prefix)), name='execute-results')}
   ${h.csrf_token(request)}
+  <br />
+  <p>
+    Please be advised, you are about to execute multiple batches!&nbsp; They will
+    be aggregated and treated as a single data source, during execution.
+  </p>
+  <br />
   % if master.has_execution_options:
       ${rendered_execution_options|n}
   % endif