#121 Error checks: check file existence before loading

[Rob Bodington]

Instead of document(file)
use:
<xsl:variable name="template_xml" select="if (doc-available($template_file)) then doc($template_file) else ()"/>
<xsl:if test="not(doc-available($template_file))">
<xsl:call-template name="error_message">
<xsl:with-param name="message"
select="concat('Error template.xml file does not exist: ', resolve-uri($template_file))"
/>
</xsl:call-template>
</xsl:if>