Backport PR to fix attribute checks

See Schematron/schematron#41

Author: Jelte Jansen

tools/convert_xsl/iso_schematron_skeleton_for_saxon.xsl

@@ -516,7 +516,10 @@ which require a preprocess.
   which I find a bit surprising but anyway I'll use the longr faster version.
 -->
 <xsl:variable name="context-xpath">
+<!--
   <xsl:if test="$attributes='true' and parent::node() ">@*|</xsl:if>
+-->
+  <xsl:if test="$attributes='true'">@*|</xsl:if>
   <xsl:choose>
     <xsl:when test="$only-child-elements='true'">*</xsl:when>
     <xsl:when test="$visit-text='true'">node()</xsl:when>