do not evaluate '<?php' line

do not evaluate '<?php' line

This happen when you are sending to eval.php a php file. The first line
is the string '<?php' which is passed to eval(). Boom!
This patch skip that string.

Example usage:
 $ cat somefile.php
 <?php
 echo "Working!\n";
 $

 $ cat somefile.php | php maintenance/eval.php
 Working!
 $