[FrameworkBundle] When there are multiple nested exceptions, this hides the stacktrace from all exceptions by default

This addresses the potential issue where a user doesn't realize that there are multiple exception messages because the
full stack trace of the first exception is displayed (pushing the others far far down the page). This hides the stacktrace
of all exceptions (when there are more than one) by default, making each exception message easily viewable.

src/Symfony/Bundle/FrameworkBundle/Resources/views/Exception/traces.html.twig

@@ -5,8 +5,8 @@
             {{ exception.class|abbr_class }}: {{ exception.message|replace({ "\n": '<br />' }) }}&nbsp;
             {% spaceless %}
             <a href="#" onclick="toggle('traces_{{ position }}', 'traces'); switchIcons('icon_traces_{{ position }}_open', 'icon_traces_{{ position }}_close'); return false;">
-                <img class="toggle" id="icon_traces_{{ position }}_close" alt="-" src="{{ asset('bundles/framework/images/blue_picto_less.gif') }}" style="visibility: {{ 0 == position ? 'display' : 'hidden' }}" />
-                <img class="toggle" id="icon_traces_{{ position }}_open" alt="+" src="{{ asset('bundles/framework/images/blue_picto_more.gif') }}" style="visibility: {{ 0 == position ? 'hidden' : 'display' }}; margin-left: -18px" />
+                <img class="toggle" id="icon_traces_{{ position }}_close" alt="-" src="{{ asset('bundles/framework/images/blue_picto_less.gif') }}" style="visibility: {{ 0 == count ? 'display' : 'hidden' }}" />
+                <img class="toggle" id="icon_traces_{{ position }}_open" alt="+" src="{{ asset('bundles/framework/images/blue_picto_more.gif') }}" style="visibility: {{ 0 == count ? 'hidden' : 'display' }}; margin-left: -18px" />
             </a>
             {% endspaceless %}
         </h2>
@@ -15,7 +15,7 @@
     {% endif %}
 
     <a id="traces_link_{{ position }}"></a>
-    <ol class="traces list_exception" id="traces_{{ position }}" style="display: {{ 0 == position ? 'block' : 'none' }}">
+    <ol class="traces list_exception" id="traces_{{ position }}" style="display: {{ 0 == count ? 'block' : 'none' }}">
         {% for i, trace in exception.trace %}
             <li>
                 {% include 'Framework:Exception:trace.html.twig' with { 'prefix': position, 'i': i, 'trace': trace } only %}