Thank you, but I had to make some modification:
PHP Code:
<input class="cmnt-buttons\" type=\"button\" onclick=\"checkAll(document.getElementById('manageposts')); return false; \" value=\"check all\" name=\"chechallbox\" />
<input class='cmnt-buttons' type='button' onclick=\"clearAll(document.getElementById('manageposts')); return false; \" value='uncheck all' name='clearallbox' />
<input class=\"cmnt-buttons\" type=\"button\" onclick=\"invertselection(document.getElementById('manageposts')); return false; \" value=\"Invert selection\" name=\"invcheckbox\" />