[Typo3-dev] Error extending EM

[Michael Scharkow]

Hi *,

I am writing an extension to suppress dotfiles and directories in the 
Extension manager. (Some people might remember the thread on how to 
_not_ include you .svn directory when uploading to TER)

The fix itself is a three-liner, but I cannot get the beast to extend 
the EM class.

this is the ext_localconf.php

<?php
if (!defined ("TYPO3_MODE"))     die ("Access denied.");
$TYPO3_CONF_VARS["BE"]["XCLASS"]["typo3/mod/tools/em/index.php"] = 
t3lib_extMgm::extPath($_EXTKEY)."class.ux_em_uploadArrayDotFix.php";
?>

no matter what I include in class.ux_em_uploadArrayDotFix.php, I always 
get an error message in EM, like

Warning: Cannot add header information - headers already sent by (output 
started at 
/var/www/ssl_3.7/typo3conf/ext/ms_em_no_dotfiles/class.ux_em_uploadArrayDotFix.php:73) 
in /var/www/ssl_3.7/typo3_src-3.7.0/typo3/template.php on line 601


I think I am missing something but I don't know what...

Any hints?

Greetings,
Michael