erp5_xhtml_style: Customise standard_error_message.

Also, reduces dependencies on zpt_* skin folders.

product/ERP5/bootstrap/erp5_xhtml_style/SkinTemplateItem/portal_skins/erp5_xhtml_style/standard_error_message.xml

+<?xml version="1.0"?>
+<ZopeData>
+  <record id="1" aka="AAAAAAAAAAE=">
+    <pickle>
+      <global name="ZopePageTemplate" module="Products.PageTemplates.ZopePageTemplate"/>
+    </pickle>
+    <pickle>
+      <dictionary>
+        <item>
+            <key> <string>_bind_names</string> </key>
+            <value>
+              <object>
+                <klass>
+                  <global name="NameAssignments" module="Shared.DC.Scripts.Bindings"/>
+                </klass>
+                <tuple/>
+                <state>
+                  <dictionary>
+                    <item>
+                        <key> <string>_asgns</string> </key>
+                        <value>
+                          <dictionary>
+                            <item>
+                                <key> <string>name_subpath</string> </key>
+                                <value> <string>traverse_subpath</string> </value>
+                            </item>
+                          </dictionary>
+                        </value>
+                    </item>
+                  </dictionary>
+                </state>
+              </object>
+            </value>
+        </item>
+        <item>
+            <key> <string>content_type</string> </key>
+            <value> <string>text/html</string> </value>
+        </item>
+        <item>
+            <key> <string>expand</string> </key>
+            <value> <int>0</int> </value>
+        </item>
+        <item>
+            <key> <string>id</string> </key>
+            <value> <string>standard_error_message</string> </value>
+        </item>
+        <item>
+            <key> <string>output_encoding</string> </key>
+            <value> <string>utf-8</string> </value>
+        </item>
+        <item>
+            <key> <string>title</string> </key>
+            <value> <unicode></unicode> </value>
+        </item>
+      </dictionary>
+    </pickle>
+  </record>
+</ZopeData>

product/ERP5/bootstrap/erp5_xhtml_style/SkinTemplateItem/portal_skins/erp5_xhtml_style/standard_error_message.zpt

+<tal:block
+  xmlns:tal="http://xml.zope.org/namespaces/tal"
+  xmlns:metal="http://xml.zope.org/namespaces/metal"
+  xmlns:i18n="http://xml.zope.org/namespaces/i18n"
+  metal:use-macro="context/main_template/macros/master"
+>
+<metal:slot metal:fill-slot="main" i18n:domain="erp5_ui">
+<div tal:condition="options/error_message" tal:content="structure options/error_message" />
+<div tal:condition="not: options/error_message">
+  <h2 i18n:translate="">Site Error</h2>
+  <p i18n:translate="">An error was encountered while publishing this resource.</p>
+  <p>
+    <strong i18n:translate="">Error Type: <span tal:replace="options/error_type" i18n:name="error_type" /></strong><br />
+    <strong i18n:translate="">Error Value: <span tal:replace="options/error_value" i18n:name="error_value" /></strong><br />
+  </p>
+  <hr noshade="noshade" />
+  <p i18n:translate="">Troubleshooting Suggestions</p>
+  <ul>
+    <li tal:condition="python: options['error_type'] in ('KeyError', 'NameError')" i18n:translate="">This resource may be trying to reference a nonexistent object or variable <strong><span tal:replace="options/error_value" i18n:name="error_value" /></strong>.</li>
+    <li i18n:translate="">The URL may be incorrect.</li>
+    <li i18n:translate="">The parameters passed to this resource may be incorrect.</li>
+    <li i18n:translate="">A resource that this resource relies on may be encountering an error.</li>
+  </ul>
+  <p i18n:translate="">For more detailed information about the error, please refer to the error log.</p>
+  <p i18n:translate="">If the error persists please contact the site maintainer. Thank you for your patience.</p>
+</div>
+<div tal:condition="options/error_log_url | nothing">
+  <hr noshade="noshade" />
+  <a href="error_log_url" tal:attributes="href options/error_log_url" i18n:translate="">Show Error Log Entry</a>
+</div>
+</metal:slot>
+</tal:block>
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