title: xmllint warns about missing space of xslt generated file
body: <p>When running xmllint on a xml file generated by xsltproc, I get the following error:</p>
  
  <pre><code>xmllint --valid --noout build/docbook/index.xml                                                         :(
  build/docbook/index.xml:1: parser error : Space needed here
  &lt;?xml version="1.0"?&gt;
                     ^ 
  </code></pre>
  
  <p>Is this space really necessary? Is this an issue of xsltproc?</p>