title: Make svn automatically detect diff-cmd and diff3-cmd depending on file extension
body: <p>In Git one can specify these in <code>.gitattributes</code> and perform some additional configuration:</p>
  
  <pre><code>git config diff.difftool.command ...
  git config merge.mergetool.driver ...
  </code></pre>
  
  <p>In Mercurial it is possible to specify patterns in <code>hgrc</code> file (<code>[diff-patterns]</code> and <code>[merge-patterns]</code> sections).</p>
  
  <p>How to achieve this in Subversion?</p>