title: PHP preg_replace backreference causing undefined constant notice
body: <p>I'm trying to use NameCase a php class on <a href="http://code.google.com/p/lastname/" rel="nofollow">code.google.com</a>.  When I run it I get this notice and I don't understand why.</p>
  
  <blockquote>
    <p>PHP Notice:  Use of undefined constant Mc - assumed 'Mc' in
    namecase.php(54) : regexp code on line 1</p>
  </blockquote>
  
  <pre><code>53   if( preg_match('/\bMac[A-Za-z]{2,}[^aciozj]\b/', $str) || preg_match('/\bMc/', $str) ) {
  54     $str = preg_replace("/\b(Ma?c)([A-Za-z]+)/e", "$1.ucfirst('\\2')", $str);
  55     // Now correct for "Mac" exceptions
  56     $str = preg_replace('/\bMacEvicius/','Macevicius', $str); // Lithuanian
  57     $str = preg_replace('/\bMacHado/',   'Machado', $str);    // Portuguese
  58     $str = preg_replace('/\bMacHar/',    'Machar', $str);
  59     ...
  </code></pre>
  
  <p>Is there anything that can be done to correct the code so it doesn't produce the notice.</p>
  
  <p>Thanks</p>