Fix getAttributeNS related comment in RelaxNG2's validateAttribute()
Make parsing methods of odf.OdfUtils deal with undefined & null values
Fix exception on  masterPageName being null in odf.StyleCache.masterPage()
Do not pass null to odf.Formatting.getMasterPageElement()
deal with possible not existing xlink:href attribute in OdfUtils.getHyperlinkTarget

as this is in a public method with no other check if the passed element
is a proper <text:a> element, better be safe then sorry
Make parsing methods of odf.StyleParseUtils deal with undefined & null values
attribute style:display-name is only optional, use style:name as fallback for display
Make odf.StyleParseUtils' lengthInPx() deal with undefined & null values