Until now all the ext_localconf.php files provided by extensions 
were included in a global scope. This is a major blocker for
a clean and flexible bootstrapping.

Include the configuration files in a method of the bootstrap class 
and set all supported global variables as global.

Resolves: #38124
Releases: 6.0
Change-Id: I4e7136d39f85258f75f6f76cb60eeede8bfc0453
Reviewed-on: http://review.typo3.org/12139
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Reviewed-by: Oliver Hader
Tested-by: Oliver Hader