TYPO3 Core

In order to have a proper "way to do things" for extension
developers to look up registration process the following
parts were streamlined:

- Discouraged usage of the pseudo-global variable
$_EXTKEY inside ext_localconf.php and ext_tables.php
in favor of strings. For module registrations this part
was left out for now as module registration will be
streamlined separately.
- Use PHP5.5-style ::class in all occurences instead
of escaped strings for class names.
- Use $GLOBALS['TYPO3_CONF_VARS'] instead of
$TYPO3_CONF_VARS.