View source for Upgrading to mediawiki 1.18

When I was upgrading my wikis to version 1.18, I encountered several problems. I resolved those problems, and to help users who run into the same issues I will document the solution here.

=First problem: after upgrading, the URL http://<site>/mw-config/index.php does not work=

When you, as per instruction in the UPGRADE readme file, browse to the URL http://<site>/mw-config/index.php, it does not show up. 

If you look into the apache error log, you will find entries like 
 PHP Fatal error:  Cannot redeclare wfprofilein() (previously declared in /srv/www/htdocs/wiki/includes/profiler/Profiler.php:14) in /s
rv/www/htdocs/wiki/includes/ProfilerStub.php on line 24
This can be fixed by editing the file 'StartProfiler.php' in your wiki root.