Boostbook: Only put table/hr in header if it has content.

Also fixed option name for 'boost.defaults' in comment.

[SVN r75837]

xsl/navbar.xsl

@@ -14,7 +14,7 @@
  
    <!--
       boost.defaults:
-        *custom  - only use explicitly set parameters
+        *none    - only use explicitly set parameters
          Boost   - use standard boost settings, can be overridden
    -->
    <xsl:param name = "boost.defaults" select = "'none'"/>
@@ -87,6 +87,7 @@
       <xsl:variable name = "home" select = "/*[1]"/>
       <xsl:variable name = "up"   select = "parent::*"/>
 
+      <xsl:if test = "boolean(normalize-space($boost.image.src)) or $nav.layout != 'none'">
          <table cellpadding = "2" width = "100%"><tr>
             <xsl:if test = "$nav.border = 'Boost'">
                <xsl:attribute name = "class">boost-head</xsl:attribute>
@@ -114,6 +115,7 @@
             </xsl:choose>
          </tr></table>
          <hr/>
+      </xsl:if>
       <xsl:choose>
          <xsl:when test = "$nav.flow = 'DocBook'">
             <table width = "100%" class = "navheader">